                                                           REC-html40-971218

                           HTML 4.0 Specification

                       W3C Recommendation 18-Dec-1997

This version:
     http://www.w3.org/TR/REC-html40-971218
Latest version:
     http://www.w3.org/TR/REC-html40
Previous version:
     http://www.w3.org/TR/PR-html40-971107
Editors:
     Dave Raggett <dsr@w3.org>
     Arnaud Le Hors <lehors@w3.org>
     Ian Jacobs <ij@w3.org>

Abstract

This specification defines the HyperText Markup Language (HTML), version
4.0, the publishing language of the World Wide Web. In addition to the text,
multimedia, and hyperlink features of the previous versions of HTML, HTML
4.0 supports more multimedia options, scripting languages, style sheets,
better printing facilities, and documents that are more accessible to users
with disabilities. HTML 4.0 also takes great strides towards the
internationalization of documents, with the goal of making the Web truly
World Wide.

HTML 4.0 is an SGML application conforming to International Standard ISO
8879 -- Standard Generalized Markup Language [ISO8879].

Status of this document

This document has been reviewed by W3C Members and other interested parties
and has been endorsed by the Director as a W3C Recommendation. It is a
stable document and may be used as reference material or cited as a
normative reference from another document. W3C's role in making the
Recommendation is to draw attention to the specification and to promote its
widespread deployment. This enhances the functionality and interoperability
of the Web.

W3C recommends that user agents and authors (and in particular, authoring
tools) produce HTML 4.0 documents rather than HTML 3.2 documents (see
[HTML32]). For reasons of backwards compatibility, W3C also recommends that
tools interpreting HTML 4.0 continue to support HTML 3.2 and HTML 2.0 as
well.

A list of current W3C Recommendations and other technical documents can be
found at http://www.w3.org/TR.

Public discussion on HTML features takes place on www-html@w3.org.

Available formats

The HTML 4.0 W3C Recommendation is also available in the following formats:

A plain text file:
     http://www.w3.org/TR/REC-html40-971218/html40.txt (723Kb),
A gzip'ed tar file containing HTML documents:
     http://www.w3.org/TR/REC-html40-971218/html40.tgz (339Kb),
A zip file containing HTML documents (this is a '.zip' file not an '.exe'):
     http://www.w3.org/TR/REC-html40-971218/html40.zip (372Kb),
A Postscript file:
     http://www.w3.org/TR/REC-html40-971218/html40.ps (4.4Mb, 363 pages),
A PDF file:
     http://www.w3.org/TR/REC-html40-971218/html40.pdf (2.1Mb) file.

In case of a discrepancy between electronic and printed forms of the
specification, the electronic version is the definitive version.

Available languages

The English version of this specification is the only normative version.
However, for translations of this document, see
http://www.w3.org/MarkUp/html40-updates/translations.html.

Errata

The list of known errors in this specification is available at
http://www.w3.org/MarkUp/html40-updates/html40-errata.html

Please report errors in this document to www-html-editor@w3.org.

Table of Contents

  1. About the HTML 4.0 Specification
       1. How the specification is organized
       2. Document conventions
            1. Elements and attributes
            2. Notes and examples
       3. Acknowledgments
       4. Copyright Notice
  2. Introduction to HTML 4.0
       1. What is the World Wide Web?
            1. Introduction to URIs
            2. Fragment identifiers
            3. Relative URIs
       2. What is HTML?
            1. A brief history of HTML
       3. HTML 4.0
            1. Internationalization
            2. Accessibility
            3. Tables
            4. Compound documents
            5. Style sheets
            6. Scripting
            7. Printing
       4. Authoring documents with HTML 4.0
            1. Separate structure and presentation
            2. Consider universal accessibility to the Web
            3. Help user agents with incremental rendering
  3. On SGML and HTML
       1. Introduction to SGML
       2. SGML constructs used in HTML
            1. Elements
            2. Attributes
            3. Character references
            4. Comments
       3. How to read the HTML DTD
            1. DTD Comments
            2. Parameter entity definitions
            3. Element declarations
                  + Content model definitions
            4. Attribute declarations
                  + DTD entities in attribute definitions
                  + Boolean attributes
  4. Conformance: requirements and recommendations
       1. Definitions
       2. SGML
       3. The text/html content type
  5. HTML Document Representation - Character sets, character encodings, and
     entities
       1. The Document Character Set
       2. Character encodings
            1. Choosing an encoding
                  + Notes on specific encodings
            2. Specifying the character encoding
       3. Character references
            1. Numeric character references
            2. Character entity references
       4. Undisplayable characters
  6. Basic HTML data types - Character data, colors, lengths, URIs, content
     types, etc.
       1. Case information
       2. SGML basic types
       3. Text strings
       4. URIs
       5. Colors
            1. Notes on using colors
       6. Lengths
       7. Content types (MIME types)
       8. Language codes
       9. Character encodings
      10. Single characters
      11. Dates and times
      12. Link types
      13. Media descriptors
      14. Script data
      15. Style sheet data
      16. Frame target names
  7. The global structure of an HTML document - The HEAD and BODY of a
     document
       1. Introduction to the structure of an HTML document
       2. HTML version information
       3. The HTML element
       4. The document head
            1. HEAD element
            2. The TITLE element
            3. The title attribute
            4. Meta data
                  + Specifying meta data
                  + The META element
                  + Meta data profiles
       5. The document body
            1. The BODY element
            2. Element identifiers: the id and class attributes
            3. Block-level and inline elements
            4. Grouping elements: the DIV and SPAN elements
            5. Headings: The H1, H2, H3, H4, H5, H6 elements
            6. The ADDRESS element
  8. Language information and text direction - International considerations
     for text
       1. Specifying the language of content: the lang attribute
            1. Language codes
            2. Inheritance of language codes
            3. Interpretation of language codes
       2. Specifying the direction of text and tables: the dir attribute
            1. Introduction to the bidirectional algorithm
            2. Inheritance of text direction information
            3. Setting the direction of embedded text
            4. Overriding the bidirectional algorithm: the BDO element
            5. Character references for directionality and joining control
            6. The effect of style sheets on bidirectionality
  9. Text - Paragraphs, Lines, and Phrases
       1. White space
       2. Structured text
            1. Phrase elements: EM, STRONG, DFN, CODE, SAMP, KBD, VAR, CITE,
               ABBR, and ACRONYM
            2. Quotations: The BLOCKQUOTE and Q elements
                  + Rendering quotations
            3. Subscripts and superscripts: the SUB and SUP elements
       3. Lines and Paragraphs
            1. Paragraphs: the P element
            2. Controlling line breaks
                  + Forcing a line break: the BR element
                  + Prohibiting a line break
            3. Hyphenation
            4. Preformatted text: The PRE element
            5. Visual rendering of paragraphs
       4. Marking document changes: The INS and DEL elements
 10. Lists - Unordered, Ordered, and Definition Lists
       1. Introduction to lists
       2. Unordered lists (UL), ordered lists (OL), and list items (LI)
       3. Definition lists: the DL, DT, and DD elements
            1. Visual rendering of lists
       4. The DIR and MENU elements
 11. Tables
       1. Introduction to tables
       2. Elements for constructing tables
            1. The TABLE element
                  + Table directionality
            2. Table Captions: The CAPTION element
            3. Row groups: the THEAD, TFOOT, and TBODY elements
            4. Column groups: the COLGROUP and COL elements
                  + The COLGROUP element
                  + The COL element
                  + Calculating the number of columns in a table
                  + Calculating the width of columns
            5. Table rows: The TR element
            6. Table cells: The TH and TD elements
                  + Cells that span several rows or columns
       3. Table formatting by visual user agents
            1. Borders and rules
            2. Horizontal and vertical alignment
                  + Inheritance of alignment specifications
            3. Cell margins
       4. Table rendering by non-visual user agents
            1. Associating header information with data cells
            2. Categorizing cells
            3. Algorithm to find heading information
       5. Sample table
 12. Links - Hypertext and Media-Independent Links
       1. Introduction to links and anchors
            1. Visiting a linked resource
            2. Other link relationships
            3. Specifying anchors and links
            4. Link titles
            5. Internationalization and links
       2. The A element
            1. Syntax of anchor names
            2. Nested links are illegal
            3. Anchors with the id attribute
            4. Unavailable and unidentifiable resources
       3. Document relationships: the LINK element
            1. Forward and reverse links
            2. Links and external style sheets
            3. Links and search engines
       4. Path information: the BASE element
            1. Resolving relative URIs
 13. Objects, Images, and Applets
       1. Introduction to objects, images, and applets
       2. Including an image: the IMG element
       3. Generic inclusion: the OBJECT element
            1. Rules for rendering objects
            2. Object initialization: the PARAM element
            3. Global naming schemes for objects
            4. Object declarations and instantiations
       4. Including an applet: the APPLET element
       5. Notes on embedded documents
       6. Image maps
            1. Client-side image maps: the MAP and AREA elements
                  + Client-side image map examples
            2. Server-side image maps
       7. Visual presentation of images, objects, and applets
            1. Width and height
            2. White space around images and objects
            3. Borders
            4. Alignment
       8. How to specify alternate text
 14. Style Sheets - Adding style to HTML documents
       1. Introduction to style sheets
       2. Adding style to HTML
            1. Setting the default style sheet language
            2. Inline style information
            3. Header style information: the STYLE element
            4. Media types
       3. External style sheets
            1. Preferred and alternate style sheets
            2. Specifying external style sheets
       4. Cascading style sheets
            1. Media-dependent cascades
            2. Inheritance and cascading
       5. Hiding style data from user agents
       6. Linking to style sheets with HTTP headers
 15. Alignment, font styles, and horizontal rules
       1. Formatting
            1. Background color
            2. Alignment
            3. Floating objects
                  + Float an object
                  + Float text around an object
       2. Fonts
            1. Font style elements: the TT, I, B, BIG, SMALL, STRIKE, S, and
               U elements
            2. Font modifier elements: FONT and BASEFONT
       3. Rules: the HR element
 16. Frames - Multi-view presentation of documents
       1. Introduction to frames
       2. Layout of frames
            1. The FRAMESET element
                  + Rows and columns
                  + Nested frame sets
                  + Sharing data among frames
            2. The FRAME element
                  + Setting the initial contents of a frame
                  + Visual rendering of a frame
       3. Specifying target frame information
            1. Setting the default target for links
            2. Target semantics
       4. Alternate content
            1. The NOFRAMES element
            2. Long descriptions of frames
       5. Inline frames: the IFRAME element
 17. Forms - User-input Forms: Text Fields, Buttons, Menus, and more
       1. Introduction to forms
       2. Controls
            1. Control types
       3. The FORM element
       4. The INPUT element
            1. Control types created with INPUT
            2. Examples of forms containing INPUT controls
       5. The BUTTON element
       6. The SELECT, OPTGROUP, and OPTION elements
            1. Preselected options
       7. The TEXTAREA element
       8. The ISINDEX element
       9. Labels
            1. The LABEL element
      10. Adding structure to forms: the FIELDSET and LEGEND elements
      11. Giving focus to an element
            1. Tabbing navigation
            2. Access keys
      12. Disabled and read-only controls
            1. Disabled controls
            2. Read-only controls
      13. Form submission
            1. Form submission method
            2. Successful controls
            3. Processing form data
                  + Step one: Identify the successful controls
                  + Step two: Build a form data set
                  + Step three: Encode the form data set
                  + Step four: Submit the encoded form data set
            4. Form content types
                  + application/x-www-form-urlencoded
                  + multipart/form-data
 18. Scripts - Animated Documents and Smart Forms
       1. Introduction to scripts
       2. Designing documents for user agents that support scripting
            1. The SCRIPT element
            2. Specifying the scripting language
                  + The default scripting language
                  + Local declaration of a scripting language
                  + References to HTML elements from a script
            3. Intrinsic events
            4. Dynamic modification of documents
       3. Designing documents for user agents that don't support scripting
            1. The NOSCRIPT element
            2. Hiding script data from user agents
 19. SGML reference information for HTML - Formal definition of HTML and
     validation
       1. document Document Validation
       2. Sample SGML catalog
 20. SGML Declaration of HTML 4.0
       1. SGML Declaration
 21. Document Type Definition
 22. Transitional Document Type Definition
 23. Frameset Document Type Definition
 24. Character entity references in HTML 4.0
       1. Introduction to character entity references
       2. Character entity references for ISO 8859-1 characters
            1. The list of characters
       3. Character entity references for symbols, mathematical symbols, and
          Greek letters
            1. The list of characters
       4. Character entity references for markup-significant and
          internationalization characters
            1. The list of characters

  A. Changes between HTML 3.2 and HTML 4.0
       1. Changes to elements
            1. New elements
            2. Deprecated elements
            3. Obsolete elements
       2. Changes to attributes
       3. Changes for accessibility
       4. Changes for meta data
       5. Changes for text
       6. Changes for links
       7. Changes for tables
       8. Changes for images, objects, and image maps
       9. Changes for forms
      10. Changes for style sheets
      11. Changes for frames
      12. Changes for scripting
      13. Changes for internationalization
  B. Performance, Implementation, and Design Notes
       1. Notes on invalid documents
       2. Special characters in URI attribute values
            1. Non-ASCII characters in URI attribute values
            2. Ampersands in URI attribute values
       3. SGML implementation notes
            1. Line breaks
            2. Specifying non-HTML data
                  + Element content
                  + Attribute values
            3. SGML features with limited support
            4. Boolean attributes
            5. Marked Sections
            6. Processing Instructions
            7. Shorthand markup
       4. Notes on helping search engines index your Web site
            1. Search robots
                  + The robots.txt file
                  + Robots and the META element
       5. Notes on tables
            1. Design rationale
                  + Dynamic reformatting
                  + Incremental display
                  + Structure and presentation
                  + Row and column groups
                  + Accessibility
            2. Recommended Layout Algorithms
                  + Fixed Layout Algorithm
                  + Autolayout Algorithm
       6. Notes on forms
            1. Incremental display
            2. Future projects
       7. Notes on scripting
            1. Reserved syntax for future script macros
                  + Current Practice for Script Macros
       8. Notes on frames
       9. Notes on accessibility
      10. Notes on security
            1. Security issues for forms

   * References
       1. Normative references
       2. Informative references
   * Index of Elements
   * Index of Attributes
   * Index

      Copyright  ©  1997 W3C (MIT, INRIA, Keio ), All Rights Reserved.

                     1 About the HTML 4.0 Specification

Contents

  1. How the specification is organized
  2. Document conventions
       1. Elements and attributes
       2. Notes and examples
  3. Acknowledgments
  4. Copyright Notice

1.1 How the specification is organized

This specification is divided into the following sections:

Sections 2 and 3: Introduction to HTML 4.0
     The introduction describes HTML's place in the scheme of the World Wide
     Web, provides a brief history of the development of HTML, highlights
     what can be done with HTML 4.0, and provides some HTML authoring tips.

     The brief SGML tutorial gives readers some understanding of HTML's
     relationship to SGML and gives summary information on how to read the
     HTML Document Type Definition (DTD).
Sections 4 - 24: HTML 4.0 reference manual
     The bulk of the reference manual consists of the HTML language
     reference, which defines all elements and attributes of the language.

     This document has been organized by topic rather than by the grammar of
     HTML. Topics are grouped into three categories: structure,
     presentation, and interactivity. Although it is not easy to divide HTML
     constructs perfectly into these three categories, the model reflects
     the HTML Working Group's experience that separating a document's
     structure from its presentation produces more effective and
     maintainable documents.

     The language reference consists of the following information:

        o What characters may appear in an HTML document.

        o Basic data types of an HTML document.

        o Elements that govern the structure of an HTML document, including
          text, lists, tables, links, and included objects, images, and
          applets.

        o Elements that govern the presentation of an HTML document,
          including style sheets, fonts, colors, rules, and other visual
          presentation, and frames for multi-windowed presentations.

        o Elements that govern interactivity with an HTML document,
          including forms for user input and scripts for active documents.

        o The SGML formal definition of HTML:
             + The SGML declaration of HTML.
             + Three DTDs: strict, transitional, and frameset.
             + The list of character references.
Appendixes
     The first appendix contains information about changes from HTML 3.2 to
     help authors and implementors with the transition to HTML 4.0. The
     second appendix contains performance and implementation notes, and is
     primarily intended to help implementors create user agents for HTML
     4.0.
References
     A list of normative and informative references.
Indexes
     Three indexes give readers rapid access to the definition of key
     concepts, elements and attributes.

1.2 Document conventions

This document has been written with two types of readers in mind: authors
and implementors. We hope the specification will provide authors with the
tools they need to write efficient, attractive, and accessible documents,
without over-exposing them to HTML's implementation details. Implementors,
however, should find all they need to build conforming user agents.

The specification may be approached in several ways:

   * Read from beginning to end. The specification begins with a general
     presentation of HTML and becomes more and more technical and specific
     towards the end.
   * Quick access to information. In order to get information about syntax
     and semantics as quickly as possible, the online version of the
     specification includes the following features:
       1. Every reference to an element or attribute is linked to its
          definition in the specification. Each element or attribute is
          defined in only one location.
       2. Every page includes links to the indexes, so you never are more
          than two links away from finding the definition of an element or
          attribute.
       3. The front pages of the three sections of the language reference
          manual extend the initial table of contents with more detail about
          each section.

1.2.1 Elements and attributes

Element names are written in upper case letters (e.g., BODY). Attribute
names are written in lower case letters (e.g., lang, onsubmit). Recall that
in HTML, element and attribute names are case-insensitive; the convention is
meant to encourage readability.

Element and attribute names in this document have been marked up and may be
rendered specially by some user agents.

Each attribute definition specifies the type of its value. If the type
allows a small set of possible values, the definition lists the set of
values, separated by a bar (|).

After the type information, each attribute definition indicates the
case-sensitivity of its values, between square brackets ("[]"). See the
section on case information for details.

1.2.2 Notes and examples

Informative notes are emphasized to stand out from surrounding text and may
be rendered specially by some user agents.

All examples illustrating deprecated usage are marked as "DEPRECATED
EXAMPLE". Deprecated examples also include recommended alternate solutions.
All examples that illustrates illegal usage are clearly marked "ILLEGAL
EXAMPLE".

Examples and notes have been marked up and may be rendered specially by some
user agents.

1.3 Acknowledgments

Thanks to everyone who has helped to author the working drafts that went
into the HTML 4.0 specification, and to all those who have sent suggestions
and corrections.

Many thanks to the Web Accessibility Initiative task force (WAI HC group)
for their work on improving the accessibility of HTML and to T.V. Raman
(Adobe) for his early work on developing accessible forms.

The authors of this specification, the members of the W3C HTML Working
Group, deserve much applause for their diligent review of this document,
their constructive comments, and their hard work: John D. Burger (MITRE),
Steve Byrne (JavaSoft), Martin J. Dürst (University of Zurich), Daniel
Glazman (Electricité de France), Scott Isaacs (Microsoft), Murray Maloney
(GRIF), Steven Pemberton (CWI), Robert Pernett (Lotus), Jared Sorensen
(Novell), Powell Smith (IBM), Robert Stevahn (HP), Ed Tecot (Microsoft),
Jeffrey Veen (HotWired), Mike Wexler (Adobe), Misha Wolf (Reuters), and
Lauren Wood (SoftQuad).

Thank you Dan Connolly (W3C) for rigorous and bountiful input as part-time
editor and thoughtful guidance as chairman of the HTML Working Group. Thank
you Sally Khudairi (W3C) for your indispensable work on press releases.

Thanks to David M. Abrahamson and Roger Price for their careful reading of
the specification and constructive comments.

Thanks to Jan Kärrman, author of html2ps for helping so much in creating the
Postscript version of the specification.

Of particular help from the W3C at Sophia-Antipolis were Janet Bertot, Bert
Bos, Stephane Boyera, Daniel Dardailler, Yves Lafon, Håkon Lie, Chris
Lilley, and Colas Nahaboo (Bull).

Lastly, thanks to Tim Berners-Lee without whom none of this would have been
possible.

1.4 Copyright Notice

Copyright © 1997 World Wide Web Consortium, (Massachusetts Institute of
Technology, Institut National de Recherche en Informatique et en
Automatique, Keio University). All Rights Reserved.

Documents on the W3C site are provided by the copyright holders under the
following license. By obtaining, using and/or copying this document, or the
W3C document from which this statement is linked, you agree that you have
read, understood, and will comply with the following terms and conditions:

Permission to use, copy, and distribute the contents of this document, or
the W3C document from which this statement is linked, in any medium for any
purpose and without fee or royalty is hereby granted, provided that you
include the following on ALL copies of the document, or portions thereof,
that you use:

  1. A link or URI to the original W3C document.
  2. The pre-existing copyright notice of the original author, if it doesn't
     exist, a notice of the form: "Copyright © World Wide Web Consortium,
     (Massachusetts Institute of Technology, Institut National de Recherche
     en Informatique et en Automatique, Keio University). All Rights
     Reserved."
  3. If it exists, the STATUS of the W3C document.

When space permits, inclusion of the full text of this NOTICE should be
provided. In addition, credit shall be attributed to the copyright holders
for any software, documents, or other items or products that you create
pursuant to the implementation of the contents of this document, or any
portion thereof.

No right to create modifications or derivatives is granted pursuant to this
license.

THIS DOCUMENT IS PROVIDED "AS IS," AND COPYRIGHT HOLDERS MAKE NO
REPRESENTATIONS OR WARRANTIES, EXPRESS OR IMPLIED, INCLUDING, BUT NOT
LIMITED TO, WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE,
NON-INFRINGEMENT, OR TITLE; THAT THE CONTENTS OF THE DOCUMENT ARE SUITABLE
FOR ANY PURPOSE; NOR THAT THE IMPLEMENTATION OF SUCH CONTENTS WILL NOT
INFRINGE ANY THIRD PARTY PATENTS, COPYRIGHTS, TRADEMARKS OR OTHER RIGHTS.

COPYRIGHT HOLDERS WILL NOT BE LIABLE FOR ANY DIRECT, INDIRECT, SPECIAL OR
CONSEQUENTIAL DAMAGES ARISING OUT OF ANY USE OF THE DOCUMENT OR THE
PERFORMANCE OR IMPLEMENTATION OF THE CONTENTS THEREOF.

The name and trademarks of copyright holders may NOT be used in advertising
or publicity pertaining to this document or its contents without specific,
written prior permission. Title to copyright in this document will at all
times remain with copyright holders.

                         2 Introduction to HTML 4.0

Contents

  1. What is the World Wide Web?
       1. Introduction to URIs
       2. Fragment identifiers
       3. Relative URIs
  2. What is HTML?
       1. A brief history of HTML
  3. HTML 4.0
       1. Internationalization
       2. Accessibility
       3. Tables
       4. Compound documents
       5. Style sheets
       6. Scripting
       7. Printing
  4. Authoring documents with HTML 4.0
       1. Separate structure and presentation
       2. Consider universal accessibility to the Web
       3. Help user agents with incremental rendering

2.1 What is the World Wide Web?

The World Wide Web (Web) is a network of information resources. The Web
relies on three mechanisms to make these resources readily available to the
widest possible audience:

  1. A uniform naming scheme for locating resources on the Web (e.g., URIs).
  2. Protocols, for access to named resources over the Web (e.g., HTTP).
  3. Hypertext, for easy navigation among resources (e.g., HTML).

The ties between the three mechanisms are apparent throughout this
specification.

2.1.1 Introduction to URIs

Every resource available on the Web -- HTML document, image, video clip,
program, etc. -- has an address that may be encoded by a Universal Resource
Identifier, or "URI".

URIs typically consist of three pieces:

  1. The naming scheme of the mechanism used to access the resource.
  2. The name of the machine hosting the resource.
  3. The name of the resource itself, given as a path.

Consider the URI that designates the current HTML specification:

   http://www.w3.org/TR/PR-html4/cover.html

This URI may be read as follows: There is a document available via the HTTP
protocol (see [RFC2068]), residing on the machine www.w3.org, accessible via
the path "/TR/PR-html4/cover.html". Other schemes you may see in HTML
documents include "mailto" for email and "ftp" for FTP.

Here is another example of a URI. This one refers to a user's mailbox:

   ...this is text...
   For all comments, please send email to
   <A href="mailto:joe@someplace.com">Joe Cool</A>.

Note. Most readers may be familiar with the term "URL" and not the term
"URI". URLs form a subset of the more general URI naming scheme.

2.1.2 Fragment identifiers

Some URIs refer to a location within a resource. This kind of URI ends with
"#" followed by an anchor identifier (called the fragment identifier). For
instance, here is a URI pointing to an anchor named section_2:

http://somesite.com/html/top.html#section_2

2.1.3 Relative URIs

A relative URI doesn't contain any naming scheme information. Its path
generally refers to a resource on the same machine as the current document.
Relative URIs may contain relative path components (e.g., ".." means one
level up in the hierarchy defined by the path), and may contain fragment
identifiers.

Relative URIsare resolved to full URIs using a base URI. As an example of
relative URI resolution, assume we have the base URI
"http://www.acme.com/support/intro.html". The relative URI in the following
markup for a hypertext link:

   <A href="suppliers.html">Suppliers</A>

would expand to the full URI "http://www.acme.com/support/suppliers.html",
while the relative URI in the following markup for an image

   <IMG src="../icons/logo.gif" alt="logo">

would expand to the full URI "http://www.acme.com/icons/logo.gif".

In HTML, URIs are used to:

   * Link to another document or resource, (see the A and LINK elements).
   * Link to an external style sheet or script (see the LINK and SCRIPT
     elements).
   * Include an image, object, or applets in a page, (see the IMG, OBJECT,
     APPLET and INPUT elements).
   * Create an image map (see the MAP and AREA elements).
   * Submit a form (see FORM).
   * Create a frame document (see the FRAME and IFRAME elements).
   * Cite an external reference (see the Q, BLOCKQUOTE, INS and DEL
     elements).
   * Refer to metadata conventions describing a document (see the HEAD
     element).

Please consult the section on the URI type for more information about URIs.

2.2 What is HTML?

To publish information for global distribution, one needs a universally
understood language, a kind of publishing mother tongue that all computers
may potentially understand. The publishing language used by the World Wide
Web is HTML (from HyperText Markup Language).

HTML gives authors the means to:

   * Publish online documents with headings, text, tables, lists, photos,
     etc.
   * Retrieve online information via hypertext links, at the click of a
     button.
   * Design forms for conducting transactions with remote services, for use
     in searching for information, making reservations, ordering products,
     etc.
   * Include spread-sheets, video clips, sound clips, and other applications
     directly in their documents.

2.2.1 A brief history of HTML

HTML was originally developed by Tim Berners-Lee while at CERN, and
popularized by the Mosaic browser developed at NCSA. During the course of
the 1990s it has blossomed with the explosive growth of the Web. During this
time, HTML has been extended in a number of ways. The Web depends on Web
page authors and vendors sharing the same conventions for HTML. This has
motivated joint work on specifications for HTML.

HTML 2.0 (November 1995, see [RFC1866]) was developed under the aegis of the
Internet Engineering Task Force (IETF) to codify common practice in late
1994. HTML+ (1993) and HTML 3.0 (1995, see [HTML30]) proposed much richer
versions of HTML. Despite never receiving consensus in standards
discussions, these drafts led to the adoption of a range new features. The
efforts of the World Wide Web Consortium's HTML Working Group to codify
common practice in 1996 resulted in HTML 3.2 (January 1997, see [HTML32]).
Changes from HTML 3.2 are summarized in Appendix A

Most people agree that HTML documents should work well across different
browsers and platforms. Achieving interoperability lowers costs to content
providers since they must develop only one version of a document. If the
effort is not made, there is much greater risk that the Web will devolve
into a proprietary world of incompatible formats, ultimately reducing the
Web's commercial potential for all participants.

Each version of HTML has attempted to reflect greater consensus among
industry players so that the investment made by content providers will not
be wasted and that their documents will not become unreadable in a short
period of time.

HTML has been developed with the vision that all manner of devices should be
able to use information on the Web: PCs with graphics displays of varying
resolution and color depths, cellular telephones, hand held devices, devices
for speech for output and input, computers with high or low bandwidth, and
so on.

2.3 HTML 4.0

HTML 4.0 extends HTML with mechanisms for style sheets, scripting, frames,
embedding objects, improved support for right to left and mixed direction
text, richer tables, and enhancements to forms, offering improved
accessibility for people with disabilities.

2.3.1 Internationalization

This version of HTML has been designed with the help of experts in the field
of internationalization, so that documents may be written in every language
and be transported easily around the world. This has been accomplished by
incorporating [RFC2070], which deals with the internationalization of HTML.

One important step has been the adoption of the ISO/IEC:10646 standard (see
[ISO10646]) as the document character set for HTML. This is the world's most
inclusive standard dealing with issues of the representation of
international characters, text direction, punctuation, and other world
language issues.

HTML now offers greater support for diverse human languages within a
document. This allows for more effective indexing of documents for search
engines, higher-quality typography, better text-to-speech conversion, better
hyphenation, etc.

2.3.2 Accessibility

As the Web community grows and its members diversify in their abilities and
skills, it is crucial that the underlying technologies be appropriate to
their specific needs. HTML has been designed to make Web pages more
accessible to those with physical limitations. HTML 4.0 developments
inspired by concerns for accessibility include:

   * Better distinction between document structure and presentation, thus
     encouraging the use of style sheets instead of HTML presentation
     elements and attributes.
   * Better forms, including the addition of access keys, the ability to
     group form controls semantically, the ability to group SELECT options
     semantically, and active labels.
   * The ability to markup a text description of an included object (with
     the OBJECT element).
   * A new client-side image map mechanism (the MAP element) that allows
     authors to integrate image and text links.
   * The requirement that alternate text accompany an image included via the
     IMG element.
   * Support for the title and lang attributes on all elements.
   * Support for the ABBR and ACRONYM elements.
   * A wider range of target media (tty, braille, etc.) for use with style
     sheets.
   * Better tables, including captions, column groups, and mechanisms to
     facilitate non-visual rendering.
   * Long descriptions of tables, images, frames, etc.

Authors who design pages with accessibility issues in mind will not only
receive the blessings of the accessibility community, but will benefit in
other ways as well: well-designed HTML documents that distinguish structure
and presentation will adapt more easily to new technologies.

Note. For more information about designing accessible HTML documents, please
consult [WAIGUIDE].

2.3.3 Tables

The new table model in HTML is based on [RFC1942]. Authors now have greater
control over structure and layout (e.g., column groups). The ability of
designers to recommend column widths allows user agents to display table
data incrementally (as it arrives) rather than waiting for the entire table
before rendering.

Note. At the time of writing, some HTML authoring tools rely extensively on
tables for formatting, which may easily cause accessibility problems.

2.3.4 Compound documents

HTML now offers a standard mechanism for embedding generic media objects and
applications in HTML documents. The OBJECT element (together with its more
specific ancestor elements IMG and APPLET) provides a mechanism for
including images, video, sound, mathematics, specialized applications, and
other objects in a document. It also allows authors to specify a hierarchy
of alternate renderings for user agents that don't support a specific
rendering.

2.3.5 Style sheets

Style sheets simplify HTML markup and largely relieve HTML of the
responsibilities of presentation. They give both authors and users control
over the presentation of documents -- font information, alignment, colors,
etc.

Style information can be specified for individual elements or groups of
elements. Style information may be specified in an HTML document or in
external style sheets.

The mechanisms for associating a style sheet with a document is independent
of the style sheet language.

Before the advent of style sheets, authors had limited control over
rendering. HTML 3.2 included a number of attributes and elements offering
control over alignment, font size, and text color. Authors also exploited
tables and images as a means for laying out pages. The relatively long time
it takes for users to upgrade their browsers means that these features will
continue to be used for some time. However, since style sheets offer more
powerful presentation mechanisms, the World Wide Web Consortium will
eventually phase out many of HTML's presentation elements and attributes.
Throughout the specification elements and attributes at risk are marked as
"deprecated". They are accompanied by examples of how to achieve the same
effects with other elements or style sheets.

2.3.6 Scripting

Through scripts, authors may create dynamic Web pages (e.g., "smart forms"
that react as users fill them out) and use HTML as a means to build
networked applications.

The mechanisms provided to include scripts in an HTML document are
independent of the scripting language.

2.3.7 Printing

Sometimes, authors will want to make it easy for users to print more than
just the current document. When documents form part of a larger work, the
relationships between them can be described using the HTML LINK element or
using W3C's Resource Description Language (RDF) (see [RDF]).

2.4 Authoring documents with HTML 4.0

We recommend that authors and implementors observe the following general
principles when working with HTML 4.0.

2.4.1 Separate structure and presentation

HTML has its roots in SGML which has always been a language for the
specification of structural markup. As HTML matures, more and more of its
presentational elements and attributes are being replaced by other
mechanisms, in particular style sheets. Experience has shown that separating
the structure of a document from its presentational aspects reduces the cost
of serving a wide range of platforms, media, etc., and facilitates document
revisions.

2.4.2 Consider universal accessibility to the Web

To make the Web more accessible to everyone, notably those with
disabilities, authors should consider how their documents may be rendered on
a variety of platforms: speech-based browsers, braille-readers, etc. We do
not recommend that authors limit their creativity, only that they consider
alternate renderings in their design. HTML offers a number of mechanisms to
this end (e.g., the alt attribute, the accesskey attribute, etc.)

Furthermore, authors should keep in mind that their documents may be
reaching a far-off audience with different computer configurations. In order
for documents to be interpreted correctly, authors should include in their
documents information about the natural language and direction of the text,
how the document is encoded, and other issues related to
internationalization.

2.4.3 Help user agents with incremental rendering

By carefully designing their tables and making use of new table features in
HTML 4.0, authors can help user agents render documents more quickly.
Authors can learn how to design tables for incremental rendering (see the
TABLE element). Implementors should consult the notes on tables in the
appendix for information on incremental algorithms.

                             3 On SGML and HTML

Contents

  1. Introduction to SGML
  2. SGML constructs used in HTML
       1. Elements
       2. Attributes
       3. Character references
       4. Comments
  3. How to read the HTML DTD
       1. DTD Comments
       2. Parameter entity definitions
       3. Element declarations
             + Content model definitions
       4. Attribute declarations
             + DTD entities in attribute definitions
             + Boolean attributes

This section of the document introduces SGML and discusses its relationship
to HTML. A complete discussion of SGML is left to the standard (see
[ISO8879]).

3.1 Introduction to SGML

SGML is a system for defining markup languages. Authors mark up their
documents by representing structural, presentational, and semantic
information alongside content. HTML is one example of a markup language.
Here is an example of an HTML document:

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0//EN"
     "http://www.w3.org/TR/REC-html40/strict.dtd">
<HTML>
   <HEAD>
      <TITLE>My first HTML document</TITLE>
   </HEAD>
   <BODY>
      <P>Hello world!
   </BODY>
</HTML>

An HTML document is divided into a head section (here, between <HEAD> and
</HEAD>) and a body (here, between <BODY> and </BODY>). The title of the
document appears in the head (along with other information about the
document), and the content of the document appears in the body. The body in
this example contains just one paragraph, marked up with <P>.

Each markup language defined in SGML is called an SGML application. An SGML
application is generally characterized by:

  1. An SGML declaration. The SGML declaration specifies which characters
     and delimiters may appear in the application.
  2. A document type definition (DTD). The DTD defines the syntax of markup
     constructs. The DTD may include additional definitions such as
     character entity references.
  3. A specification that describes the semantics to be ascribed to the
     markup. This specification also imposes syntax restrictions that cannot
     be expressed within the DTD.
  4. Document instances containing data (content) and markup. Each instance
     contains a reference to the DTD to be used to interpret it.

The HTML 4.0 specification includes an SGML declaration, three document type
definitions (see the section on HTML version information for a description
of the three), and a list of character references.

3.2 SGML constructs used in HTML

The following sections introduce SGML constructs that are used in HTML.

The appendix lists some SGML features that are not widely supported by HTML
tools and user agents and should be avoided.

3.2.1 Elements

An SGML document type definition declares element types that represent
structures or desired behavior. HTML includes element types that represent
paragraphs, hypertext links, lists, tables, images, etc.

Each element type declaration generally describes three parts: a start tag,
content, and an end tag.

The element's name appears in the start tag (written <element-name>) and the
end tag (written </element-name>); note the slash before the element name in
the end tag. For example, the start and end tags of the UL element type
delimit the items in a list:

<UL>
<LI><P>...list item 1...
<LI><P>...list item 2...
</UL>

Some HTML element types allow authors to omit end tags (e.g., the P and LI
element types). A few element types also allow the start tags to be omitted;
for example, HEAD and BODY. The HTML DTD indicates for each element type
whether the start tag and end tag are required.

Some HTML element types have no content. For example, the line break element
BR has no content; its only role is to terminate a line of text. Such empty
elements never have end tags. The document type definition and the text of
the specification indicate whether an element type is empty (has no content)
or, if it can have content, what is considered legal content.

Element names are always case-insensitive.

Please consult the SGML standard for information about rules governing
elements (e.g., they must be properly nested, an end tag closes all omitted
start tags up to the matching start tag (section 7.5.1), etc.).

For example, the following paragraph:

<P>This is the first paragraph.</P>
...a block element...

may be rewritten without its end tag:

<P>This is the first paragraph.
...a block element...

since the <P> start tag is closed by the following block element. Similarly,
if a paragraph is enclosed by a block element, as in:

<DIV>
<P>This is the paragraph.
</DIV>

the end tag of the enclosing block element (here, </DIV>) implies the end
tag of the open <P> start tag.

Elements are not tags. Some people refer to elements as tags (e.g., "the P
tag"). Remember that the element is one thing, and the tag (be it start or
end tag) is another. For instance, the HEAD element is always present, even
though both start and end HEAD tags may be missing in the markup.

All the element types declared in this specification are listed in the
element index.

3.2.2 Attributes

Elements may have associated properties, called attributes, which may have
values (by default, or set by authors or scripts). Attribute/value pairs
appear before the final ">" of an element's start tag. Any number of (legal)
attribute value pairs, separated by spaces, may appear in an element's start
tag. They may appear in any order.

In this example, the id attribute is set for an H1 element:

<H1 id="section1">
This is an identified heading thanks to the id attribute
</H1>

By default, SGML requires that all attribute values be delimited using
either double quotation marks (ASCII decimal 34) or single quotation marks
(ASCII decimal 39). Single quote marks can be included within the attribute
value when the value is delimited by double quote marks, and vice versa.
Authors may also use numeric character references to represent double quotes
(&#34;) and single quotes (&#39;). For double quotes authors can also use
the character entity reference &quot;.

In certain cases, authors may specify the value of an attribute without any
quotation marks. The attribute value may only contain letters (a-z and A-Z),
digits (0-9), hyphens (ASCII decimal 45), and periods (ASCII decimal 46). We
recommend using quotation marks even when it is possible to eliminate them.

Attribute names are always case-insensitive

Attribute values are generally case-insensitive. The definition of each
attribute in the reference manual indicates whether its value is
case-insensitive.

All the attributes defined by this specification are listed in the attribute
index.

3.2.3 Character references

Character references are numeric or symbolic names for characters that may
be included in an HTML document. They are useful for referring to rarely
used characters, or those that authoring tools make it difficult or
impossible to enter. You will see character references throughout this
document; they begin with a "&" sign and end with a semi-colon (;). Some
common examples include:

   * "&lt;" represents the < sign.
   * "&gt;" represents the > sign.
   * "&quot;" represents the " mark.
   * "&#229;" (in decimal) represents the letter "a" with a small circle
     above it.
   * "&#1048;" (in decimal) represents the Cyrillic capital letter "I".
   * "&#x6C34;" (in hexadecimal) represents the Chinese character for water.

We discuss HTML character references in detail later in the section on the
HTML document character set. The specification also contains a list of
character references that may appear in HTML 4.0 documents.

3.2.4 Comments

HTML comments have the following syntax:

<!-- this is a comment -->
<!-- and so is this one,
    which occupies more than one line -->

White space is not permitted between the markup declaration open
delimiter("<!") and the comment open delimiter ("--"), but is permitted
between the comment close delimiter ("--") and the markup declaration close
delimiter (">"). A common error is to include a string of hyphens ("---")
within a comment. Authors should avoid putting two or more adjacent hyphens
inside comments.

Information that appears between comments has no special meaning (e.g.,
character references are not interpreted as such).

3.3 How to read the HTML DTD

Each element and attribute declaration in this specification is accompanied
by its document type definition fragment. We have chosen to include the DTD
fragments in the specification rather than seek a more approachable, but
longer and less precise means of describing an element's properties. The
following tutorial should allow readers unfamiliar with SGML to read the DTD
and understand the technical details of the HTML specification.

3.3.1 DTD Comments

In DTDs, comments may spread over one or more lines. In the DTD, comments
are delimited by a pair of "--" marks, e.g.

<!ELEMENT PARAM - O EMPTY       -- named property value -->

Here, the comment "named property value" explains the use of the PARAM
element type. Comments in the DTD are informative only.

3.3.2 Parameter entity definitions

The HTML DTD begins with a series of parameter entity definitions. A
parameter entity definition defines a kind of macro that may be referenced
and expanded elsewhere in the DTD. These macros may not appear in HTML
documents, only in the DTD. Other types of macros, called character
references, may be used in the text of an HTML document or within attribute
values.

When the parameter entity is referred to by name in the DTD, it is expanded
into a string.

A parameter entity definition begins with the keyword <!ENTITY % followed by
the entity name, the quoted string the entity expands to, and finally a
closing >. Instances of parameter entities in a DTD begin with "%", then the
parameter entity name, and terminated by an optional ";".

The following example defines the string that the "%fontstyle;" entity will
expand to.

<!ENTITY % fontstyle "TT | I | B | BIG | SMALL">

The string the parameter entity expands to may contain other parameter
entity names. These names are expanded recursively. In the following
example, the "%inline;" parameter entity is defined to include the
"%fontstyle;", "%phrase;", "%special;" and "%formctrl;" parameter entities.

<!ENTITY % inline "#PCDATA | %fontstyle; | %phrase; | %special; | %formctrl;">

You will encounter two DTD entities frequently in the HTML DTD: "%block;"
"%inline;". They are used when the content model includes block-level and
inline elements, respectively (defined in the section on the global
structure of an HTML document).

3.3.3 Element declarations

The bulk of the HTML DTD consists of the declarations of element types and
their attributes. The <!ELEMENT keyword begins a declaration and the >
character ends it. Between these are specified:

  1. The element's name.
  2. Whether the element's end tag is optional Two hyphens that appear after
     the element name mean that the start and end tags are mandatory. One
     hyphen followed by the letter "O" indicates that the end tag can be
     omitted. A pair of letter "O"s indicate that both the start and end
     tags can be omitted.
  3. The element's content, if any. The allowed content for an element is
     called its content model. Element types that are designed to have no
     content are called empty elements elements. The content model for such
     element types is declared using the keyword "EMPTY".

In this example:

    <!ELEMENT UL - - (LI)+>

   * The element type being declared is UL.
   * The two hyphens indicate that both the start tag <UL> and the end tag
     </UL> for this element type are required.
   * The content model for this element type is declared to be "at least one
     LI element". Below, we explain how to specify content models.

This example illustrates the declaration of an empty element type:

    <!ELEMENT IMG - O EMPTY>

   * The element type being declared is IMG.
   * The hyphen and the following "O" indicate that the end tag can be
     omitted, but together with the content model "EMPTY", this is
     strengthened to the rule that the end tag must be omitted.
   * The "EMPTY" keyword means that instances of this type must not have
     content.

Content model definitions

The content model describes what may be contained by an instance of an
element type. Content model definitions may include:

   * The names of allowed or forbidden element types (e.g., the UL element
     contains instances of the LI element type, and the P element type may
     not contain other P elements).
   * DTD entities (e.g., the LABEL element contains instances of the
     "%inline;" parameter entity).
   * Document text (indicated by the SGML construct "#PCDATA"). Text may
     contain character references. Recall that these begin with & and end
     with a semicolon (e.g., "Herg&eacute;'s adventures of Tintin" contains
     the character entity reference for the "e acute" character).

The content model of an element is specified with the following syntax:

( ... )
     Delimits a group.
A | B
     Either A or B occurs, but not both.
A , B
     Both A and B occur, in that order.
A & B
     Both A and B occur, in any order.
A?
     A occurs zero or one time.
A*
     A occurs zero or more times.
A+
     A occurs one or more times.

Here are some examples from the HTML DTD:

   <!ELEMENT UL - - (LI)+>

The UL element must contain one or more LI elements.

   <!ELEMENT DL    - - (DT|DD)+>

The DL element must contain one or more DT or DD elements in any order.

   <!ELEMENT OPTION - O (#PCDATA)>

The OPTION element may only contain text and entities, such as &amp; -- this
is indicated by the SGML data type #PCDATA.

A few HTML element types use an additional SGML feature to exclude elements
from content model. Excluded elements are preceded by a hyphen. Explicit
exclusions override permitted elements.

In this example, the -(A) signifies that the element A cannot appear in
another A element (i.e., anchors may not be nested).

   <!ELEMENT A - - (%inline;)* -(A)>

Note that the A element type is part of the DTD parameter entity "%inline;",
but is excluded explicitly because of -(A).

Similarly, the following element type declaration for FORM prohibits nested
forms:

   <!ELEMENT FORM - - (%block;|SCRIPT)+ -(FORM)>

3.3.4 Attribute declarations

The <!ATTLIST keyword begins the declaration of attributes that an element
may take. It is followed by the name of the element in question, a list of
attribute definitions, and a closing >. Each attribute definition is a
triplet that defines:

   * The name of an attribute.
   * The type of the attribute's value or an explicit set of possible
     values. Values defined explicitly by the DTD are case-insensitive.
     Please consult the section on basic HTML data types for more
     information about attribute value types.
   * Whether the default value of the attribute is implicit (keyword
     "#IMPLIED"), in which case the default value must be supplied by the
     user agent (in some cases via inheritance from parent elements); always
     required (keyword "#REQUIRED"); or fixed to the given value (keyword
     "#FIXED"). Some attribute definitions explicitly specify a default
     value for the attribute.

In this example, the name attribute is defined for the MAP element. The
attribute is optional for this element.

<!ATTLIST MAP
  name        CDATA     #IMPLIED
  >

The type of values permitted for the attribute is given as CDATA, an SGML
data type. CDATA is text that may contain character references.

For more information about "CDATA", "NAME", "ID", and other data types,
please consult the section on HTML data types.

The following examples illustrate several attribute definitions:

rowspan     NUMBER     1         -- number of rows spanned by cell --
http-equiv  NAME       #IMPLIED  -- HTTP response header name  --
id          ID         #IMPLIED  -- document-wide unique id --
valign      (top|middle|bottom|baseline) #IMPLIED

The rowspan attribute requires values of type NUMBER. The default value is
given explicitly as "1". The optional http-equiv attribute requires values
of type NAME. The optional id attribute requires values of type ID. The
optional valign attribute is constrained to take values from the set {top,
middle, bottom, baseline}.

DTD entities in attribute definitions

Attribute definitions may also contain parameter entity references.

In this example, we see that the attribute definition list for the LINK
element begins with the "%attrs;" parameter entity.

<!ELEMENT LINK - O EMPTY               -- a media-independent link -->
<!ATTLIST LINK
  %attrs;                              -- %coreattrs, %i18n, %events --
  charset     %Charset;      #IMPLIED  -- char encoding of linked resource --
  href        %URI;          #IMPLIED  -- URI for linked resource --
  hreflang    %LanguageCode; #IMPLIED  -- language code --
  type        %ContentType;  #IMPLIED  -- advisory content type --
  rel         %LinkTypes;    #IMPLIED  -- forward link types --
  rev         %LinkTypes;    #IMPLIED  -- reverse link types --
  media       %MediaDesc;    #IMPLIED  -- for rendering on these media --
  >

Start tag: required, End tag: forbidden

The "%attrs;" parameter entity is defined as follows:

<!ENTITY % attrs "%coreattrs; %i18n; %events;">

The "%coreattrs;" parameter entity in the "%attrs;" definition expands as
follows:

<!ENTITY % coreattrs
 "id          ID             #IMPLIED  -- document-wide unique id --
  class       CDATA          #IMPLIED  -- space separated list of classes --
  style       %StyleSheet;   #IMPLIED  -- associated style info --
  title       %Text;         #IMPLIED  -- advisory title/amplification --"
  >

The "%attrs;" parameter entity has been defined for convenience since these
attributes are defined for most HTML element types.

Similarly, the DTD defines the "%URI;" parameter entity as expanding into
the string "CDATA".

<!ENTITY % URI "CDATA"
    -- a Uniform Resource Identifier,
       see [URI]
    -->

As this example illustrates, the parameter entity "%URI;" provides readers
of the DTD with more information as to the type of data expected for an
attribute. Similar entities have been defined for "%Color;", "%Charset;",
"%Length;", "%Pixels;", etc.

Boolean attributes

Some attributes play the role of boolean variables (e.g., the selected
attribute for the OPTION element). Their appearance in the start tag of an
element implies that the value of the attribute is "true". Their absence
implies a value of "false".

Boolean attributes may legally take a single value: the name of the
attribute itself (e.g., selected="selected").

This example defines the selected attribute to be a boolean attribute.

selected     (selected)  #IMPLIED  -- reduced inter-item spacing --

The attribute is set to "true" by appearing in the element's start tag:

<OPTION selected="selected">
...contents...
<OPTION>

In HTML, boolean attributes may be appear in minimized form -- the
attribute's value appears alone in the element's start tag. Thus, selected
may be set by writing:

<OPTION selected>

instead of:

<OPTION selected="selected">

Authors should be aware than many user agents only recognize the minimized
form of boolean attributes and not the full form.

               4 Conformance: requirements and recommendations

Contents

  1. Definitions
  2. SGML
  3. The text/html content type

In this section, we begin the specification of HTML 4.0, starting with the
contract between authors, documents, users, and user agents.

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. However, for
readability, these words do not appear in all upper case letters in this
specification.

At times, the authors of this specification recommend good practice for
authors and user agents. These recommendations are not normative and
conformance with this specification does not depend on their realization.
These recommendations contain the expression "We recommend ...", "This
specification recommends ...", or some similar wording.

4.1 Definitions

HTML document
     An HTML document is an SGML document that meets the constraints of this
     specification.
Author
     An author is a person or program that writes or generates HTML
     documents. An authoring tool is a special case of an author, namely,
     it's a program that generates HTML.

     We recommend that authors write documents that conform to the strict
     DTD rather than the other DTDs defined by this specification. Please
     see the section on version information for details about the DTDs
     defined in HTML 4.0.
User
     A user is a person who interacts with a user agent to view, hear, or
     otherwise use a rendered HTML document.
HTML user agent
     An HTML user agent is any device that interprets HTML documents. User
     agents include visual browsers (text-only and graphical), non-visual
     browsers (audio, Braille), search robots, proxies, etc.

     A conforming user agent for HTML 4.0 is one that observes the mandatory
     conditions ("must") set forth in this specification, including the
     following points:
        o A user agent should avoid imposing arbitrary length limits on
          attribute value literals (see the section on capacities in the
          SGML Declaration). For introductory information on SGML
          attributes, please consult the section on attribute definitions.
        o A user agent must ensure that rendering is unchanged by the
          presence or absence of start tags and end tags when the HTML DTD
          indicates that these are optional. See the section on element
          definitions for introductory information on SGML elements.
        o For reasons of backwards compatibility, we recommend that tools
          interpreting HTML 4.0 continue to support HTML 3.2 (see [HTML32])
          and HTML 2.0 (see [RFC1866]).
Error conditions
     This specification does not define how conforming user agents handle
     general error conditions, including how user agents behave when they
     encounter elements, attributes, attribute values, or entities not
     specified in this document.

     However, for recommended error handling behavior, please consult the
     notes on invalid documents.
Deprecated
     A deprecated element or attribute is one that has been outdated by
     newer constructs. Deprecated elements are defined in the reference
     manual in appropriate locations, but are clearly marked as deprecated.
     Deprecated elements may become obsolete in future versions of HTML.

     User agents should continue to support deprecated elements for reasons
     of backward compatibility.

     Definitions of elements and attributes clearly indicate which are
     deprecated.

     This specification includes examples that illustrate how to avoid using
     deprecated elements. In most cases these depend on user agent support
     for style sheets. In general, authors should use style sheets to
     achieve stylistic and formatting effects rather than HTML
     presentational attributes. HTML presentational attributes have been
     deprecated when style sheet alternatives exist (see, for example,
     [CSS1]).
Obsolete
     An obsolete element or attribute is one for which there is no guarantee
     of support by a user agent. Obsolete elements are no longer defined in
     the specification, but are listed for historical purposes in the
     changes section of the reference manual.

4.2 SGML

HTML 4.0 is an SGML application conforming to International Standard ISO
8879 -- Standard Generalized Markup Language SGML (defined in [ISO8879]).

Examples in the text conform to the strict document type definition unless
the example in question refers to elements or attributes only defined by the
transitional document type definition or frameset document type definition.
For the sake of brevity, most of the examples in this specification do not
begin with the document type declaration that is mandatory at the beginning
of each HTML document.

DTD fragments in element definitions come from the strict document type
definition except for the elements related to frames.

Please consult the section on HTML version information for details about
when to use the strict, transitional, or frameset DTD.

Comments appearing in the HTML 4.0 DTD have no normative value; they are
informative only.

User agents must not render SGML processing instructions (e.g., <?full
volume>) or comments. For more information about this and other SGML
features that may be legal in HTML but aren't widely supported by HTML user
agents, please consult the section on SGML features with limited support.

4.3 The text/html content type

HTML documents are sent over the Internet as a sequence of bytes accompanied
by encoding information (described in the section on character encodings).
The structure of the transmission, termed a message entity, is defined by
[RFC2045]) and [RFC2068]. A message entity with a content type of
"text/html" represents an HTML document.

The content type for HTML documents is defined as follows:

Content type name:
     text
Content subtype name:
     html
Required parameters:
     none
Optional parameters:
     charset
Encoding considerations:
     any encoding is allowed
Security considerations:
     See the notes on security

The optional parameter "charset" refers to the character encoding used to
represent the HTML document as a sequence of bytes. Legal values for this
parameter are defined in the section on character encodings. Although this
parameter is optional, we recommend that it always be present.

                       5 HTML Document Representation

Contents

  1. The Document Character Set
  2. Character encodings
       1. Choosing an encoding
             + Notes on specific encodings
       2. Specifying the character encoding
  3. Character references
       1. Numeric character references
       2. Character entity references
  4. Undisplayable characters

In this chapter, we discuss how HTML documents are represented on a computer
and over the Internet.

The section on the document character set addresses the issue of what
abstract characters may be part of an HTML document. Characters include the
Latin letter "A", the Cyrillic letter "I", the Chinese character meaning
"water", etc.

The section on character encodings addresses the issue of how those
characters may be represented in a file or when transferred over the
Internet. As some character encodings cannot directly represent all
characters an author may want to include in a document, HTML offers other
mechanisms, called character references, for referring to any character.

Since there are a great number of characters throughout human languages, and
a great variety of ways to represent those characters, proper care must be
taken so that documents may be understood by user agents around the world.

5.1 The Document Character Set

To promote interoperability, SGML requires that each application (including
HTML) specify its document character set. A document character set consists
of:

   * A Repertoire: A set of abstract characters,, such as the Latin letter
     "A", the Cyrillic letter "I", the Chinese character meaning "water",
     etc.
   * Code positions: A set of integer references to characters in the
     repertoire.

Each SGML document (including each HTML document) is a sequence of
characters from the repertoire. Computer systems identify each character by
its code position; for example, in the ASCII character set, code positions
65, 66, and 67 refer to the characters 'A', 'B', and 'C', respectively.

The ASCII character set is not sufficient for a global information system
such as the Web, so HTML uses the much more complete character set called
the Universal Character Set (UCS), defined in [ISO10646]. This standard
defines a repertoire of thousands of characters used by communities all over
the world.

The character set defined in [ISO10646] is character-by-character equivalent
to Unicode 2.0 ([UNICODE]). Both of these standards are updated from time to
time with new characters, and the amendments should be consulted at the
respective Web sites. In the current specification, references to
ISO/IEC-10646 or Unicode imply the same document character set. However, the
HTML specification also refers to the Unicode specification for other issues
such as the bidirectional text algorithm.

The document character set, however, does not suffice to allow user agents
to correctly interpret HTML documents as they are typically exchanged --
encoded as a sequence of bytes in a file or during a network transmission.
User agents must also know the specific character encoding that was used to
transform the document character stream into a byte stream.

5.2 Character encodings

What this specification calls a character encoding is known by different
names in other specifications (which may cause some confusion). However, the
concept is largely the same across the Internet. Also, protocol headers,
attributes, and parameters referring to character encodings share the same
name -- "charset" -- and use the same values from the [IANA] registry (see
[CHARSETS] for a complete list).

The "charset" parameter identifies a character encoding, which is a method
of converting a sequence of bytes into a sequence of characters. This
conversion fits naturally with the scheme of Web activity: servers send HTML
documents to user agents as a stream of bytes; user agents interpret them as
a sequence of characters. The conversion method can range from simple
one-to-one correspondence to complex switching schemes or algorithms.

A simple one-byte-per-character encoding technique is not sufficient for
text strings over a character repertoire as large as [ISO10646]. There are
several different encodings of parts of [ISO10646] in addition to encodings
of the entire character set (such as UCS-4).

5.2.1 Choosing an encoding

Authoring tools (e.g., text editors) may encode HTML documents in the
character encoding of their choice, and the choice largely depends on the
conventions used by the system software. These tools may employ any
convenient encoding that covers most of the characters contained in the
document, provided the encoding is correctly labeled. Occasional characters
that fall outside this encoding may still be represented by character
references. These always refer to the document character set, not the
character encoding.

Servers and proxies may change a character encoding (called transcoding) on
the fly to meet the requests of user agents (see section 14.2 of [RFC2068],
the "Accept-Charset" HTTP request header). Servers and proxies do not have
to serve a document in a character encoding that covers the entire document
character set.

Commonly used character encodings on the Web include ISO-8859-1 (also
referred to as "Latin-1"; usable for most Western European languages),
ISO-8859-5 (which supports Cyrillic), SHIFT_JIS (a Japanese encoding),
EUC-JP (another Japanese encoding), and UTF-8 (an encoding of ISO 10646
using a different number of bytes for different characters). Names for
character encodings are case-insensitive, so that for example "SHIFT_JIS",
"Shift_JIS", and "shift_jis" are equivalent.

This specification does not mandate which character encodings a user agent
must support.

Conforming user agents must correctly map to Unicode all characters in any
character encodings that they recognize (or they must behave as if they
did).

Notes on specific encodings

When HTML text is transmitted in UTF-16 (charset=UTF-16), text data should
be transmitted in network byte order ("big-endian", high-order byte first)
in accordance with [ISO10646], Section 6.3 and [UNICODE], clause C3, page
3-1.

Furthermore, to maximize chances of proper interpretation, it is recommended
that documents transmitted as UTF-16 always begin with a ZERO-WIDTH
NON-BREAKING SPACE character (hexadecimal FEFF, also called Byte Order Mark
(BOM)) which, when byte-reversed, becomes hexadecimal FFFE, a character
guaranteed never to be assigned. Thus, a user-agent receiving a hexadecimal
FFFE as the first bytes of a text would know that bytes have to be reversed
for the remainder of the text.

The UTF-1 transformation format of [ISO10646] (registered by IANA as
ISO-10646-UTF-1), should not be used. For information about ISO 8859-8 and
the bidirectional algorithm, please consult the section on bidirectionality
and character encoding.

5.2.2 Specifying the character encoding

How does a server determine which character encoding applies for a document
it serves? Some servers examine the first few bytes of the document, or
check against a database of known files and encodings. Many modern servers
give Web masters more control over charset configuration than old servers
do. Web masters should use these mechanisms to send out a "charset"
parameter whenever possible, but should take care not to identify a document
with the wrong "charset" parameter value.

How does a user agent know which character encoding has been used? The
server should provide this information. The most straightforward way for a
server to inform the user agent about the character encoding of the document
is to use the "charset" parameter of the "Content-Type" header field of the
HTTP protocol ([RFC2068], sections 3.4 and 14.18) For example, the following
HTTP header announces that the character encoding is EUC-JP:

Content-Type: text/html; charset=EUC-JP

Please consult the section on conformance for the definition of text/html.

The HTTP protocol ([RFC2068], section 3.7.1) mentions ISO-8859-1 as a
default character encoding when the "charset" parameter is absent from the
"Content-Type" header field. In practice, this recommendation has proved
useless because some servers don't allow a "charset" parameter to be sent,
and others may not be configured to send the parameter. Therefore, user
agents must not assume any default value for the "charset" parameter.

To address server or configuration limitations, HTML documents may include
explicit information about the document's character encoding; the META
element can be used to provide user agents with this information.

For example, to specify that the character encoding of the current document
is "EUC-JP", a document should include the following META declaration:

<META http-equiv="Content-Type" content="text/html; charset=EUC-JP">

The META declaration must only be used when the character encoding is
organized such that ASCII characters stand for themselves (at least until
the META element is parsed). META declarations should appear as early as
possible in the HEAD element.

For cases where neither the HTTP protocol nor the META element provides
information about the character encoding of a document, HTML also provides
the charset attribute on several elements. By combining these mechanisms, an
author can greatly improve the chances that, when the user retrieves a
resource, the user agent will recognize the character encoding.

To sum up, conforming user agents must observe the following priorities when
determining a document's character encoding (from highest priority to
lowest):

  1. An HTTP "charset" parameter in a "Content-Type" field.
  2. A META declaration with "http-equiv" set to "Content-Type" and a value
     set for "charset".
  3. The charset attribute set on an element that designates an external
     resource.

In addition to this list of priorities, the user agent may use heuristics
and user settings. For example, many user agents use a heuristic to
distinguish the various encodings used for Japanese text. Also, user agents
typically have a user-definable, local default character encoding which they
apply in the absence of other indicators.

User agents may provide a mechanism that allows users to override incorrect
"charset" information. However, if a user agent offers such a mechanism, it
should only offer it for browsing and not for editing, to avoid the creation
of Web pages marked with an incorrect "charset" parameter.

Note. If, for a specific application, it becomes necessary to refer to
characters outside [ISO10646], characters should be assigned to a private
zone to avoid conflicts with present or future versions of the standard.
This is highly discouraged, however, for reasons of portability.

5.3 Character references

A given character encoding may not be able to express all characters of the
document character set. For such encodings, or when hardware or software
configurations do not allow users to input some document characters
directly, authors may use SGML character references. Character references
are a character encoding-independent mechanism for entering any character
from the document character set.

Character references in HTML may appear in two forms:

   * Numeric character references (either decimal or hexadecimal).
   * Character entity references.

Character references within comments have no special meaning; they are
comment data only.

Note. HTML provides other ways to present character data, in particular
inline images.

Note. In SGML, it is possible to eliminate the final ";" after a character
reference in some cases (e.g., at a line break or immediately before a tag).
In other circumstances it may not be eliminated (e.g., in the middle of a
word). We strongly suggest using the ";" in all cases to avoid problems with
user agents that require this character to be present.

5.3.1 Numeric character references

Numeric character references specify the code position of a character in the
document character set. Numeric character references may take two forms:

   * The syntax "&#D;", where D is a decimal number, refers to the Unicode
     decimal character number D.
   * The syntax "&#xH;" or "&#XH;", where H is an hexadecimal number, refers
     to the Unicode hexadecimal character number H. Hexadecimal numbers in
     numeric character references are case-insensitive.

Here are some examples of numeric character references:

   * &#229; (in decimal) represents the letter "a" with a small circle above
     it (used, for example, in Norwegian).
   * &#xE5; (in hexadecimal) represents the same character.
   * &#Xe5; (in hexadecimal) represents the same character as well.
   * &#1048; (in decimal) represents the Cyrillic capital letter "I".
   * &#x6C34; (in hexadecimal) represents the Chinese character for water.

Note. Although the hexadecimal representation is not defined in [ISO8879],
it is expected to be in the revision, as described in [WEBSGML]. This
convention is particularly useful since character standards generally use
hexadecimal representations.

5.3.2 Character entity references

In order to give authors a more intuitive way of referring to characters in
the document character set, HTML offers a set of character entity
references. Character entity references use symbolic names so that authors
need not remember code positions. For example, the character entity
reference &aring; refers to the lower case "a" character topped with a ring;
"&aring;" is easier to remember than &#229;.

HTML 4.0 does not define a character entity reference for every character in
the document character set. For instance, there is no character entity
reference for the Cyrillic capital letter "I". Please consult the full list
of character references defined in HTML 4.0.

Character entity references are case-sensitive. Thus, &Aring; refers to a
different character (upper case A, ring) than &aring; (lower case a, ring).

Four character entity references deserve special mention since they are
frequently used to escape special characters:

   * "&lt;" represents the < sign.
   * "&gt;" represents the > sign.
   * "&amp;" represents the & sign.
   * "&quot; represents the " mark.

Authors wishing to put the "<" character in text should use "&lt;" (ASCII
decimal 60) to avoid possible confusion with the beginning of a tag (start
tag open delimiter). Similarly, authors should use "&gt;" (ASCII decimal 62)
in text instead of ">" to avoid problems with older user agents that
incorrectly perceive this as the end of a tag (tag close delimiter) when it
appears in quoted attribute values.

Authors should use "&amp;" (ASCII decimal 38) instead of "&" to avoid
confusion with the beginning of a character reference (entity reference open
delimiter). Authors should also use "&amp;" in attribute values since
character references are allowed within CDATA attribute values.

Some authors use the character entity reference "&quot;" to encode instances
of the double quote mark (") since that character may be used to delimit
attribute values.

5.4 Undisplayable characters

A user agent may not be able to render all characters in a document
meaningfully, for instance, because the user agent lacks a suitable font, a
character has a value that may not be expressed in the user agent's internal
character encoding, etc.

Because there are many different things that may be done in such cases, this
document does not prescribe any specific behavior. Depending on the
implementation, undisplayable characters may also be handled by the
underlying display system and not the application itself. In the absence of
more sophisticated behavior, for example tailored to the needs of a
particular script or language, we recommend the following behavior for user
agents:

  1. Adopt a clearly visible, but unobtrusive mechanism to alert the user of
     missing resources.
  2. If missing characters are presented using their numeric representation,
     use the hexadecimal (not decimal) form since this is the form used in
     character set standards.

                           6 Basic HTML data types

Contents

  1. Case information
  2. SGML basic types
  3. Text strings
  4. URIs
  5. Colors
       1. Notes on using colors
  6. Lengths
  7. Content types (MIME types)
  8. Language codes
  9. Character encodings
 10. Single characters
 11. Dates and times
 12. Link types
 13. Media descriptors
 14. Script data
 15. Style sheet data
 16. Frame target names

This section of the specification describes the basic data types that may
appear as an element's content or an attribute's value.

For introductory information about reading the HTML DTD, please consult the
SGML tutorial.

6.1 Case information

Each attribute definition includes information about the case-sensitivity of
its values. The case information is presented with the following keys:

CS
     The value is case-sensitive (i.e., user agents interpret "a" and "A"
     differently).
CI
     The value is case-insensitive (i.e., user agents interpret "a" and "A"
     as the same).
CN
     The value is not subject to case changes, e.g., because it is a number
     or a character from the document character set.
CA
     The element or attribute definition itself gives case information.
CT
     Consult the type definition for details about case-sensitivity.

If an attribute value is a list, the keys apply to every value in the list,
unless otherwise indicated.

6.2 SGML basic types

The document type definition specifies the syntax of HTML element content
and attribute values using SGML tokens (e.g., PCDATA, CDATA, NAME, ID,
etc.). See [ISO8879] for their full definitions. The following is a summary
of key information:

   * CDATA is a sequence of characters from the document character set and
     may include character entities. User agents should interpret attribute
     values as follows:
        o Replace character entities with characters,
        o Ignore line feeds,
        o Replace each carriage return or tab with a single space.

     User agents may ignore leading and trailing white space in CDATA
     attribute values (e.g., "   myval   " may be interpreted as "myval").
     Authors should not declare attribute values with leading or trailing
     white space.

     For some HTML 4.0 attributes with CDATA attribute values, the
     specification imposes further constraints on the set of legal values
     for the attribute that may not be expressed by the DTD.

     Although the STYLE and SCRIPT elements use CDATA for their data model,
     for these elements, CDATA must be handled differently by user agents.
     Markup and entities must be treated as raw text and passed to the
     application as is. The first occurrence of the character sequence "</"
     (end-tag open delimiter) is treated as terminating the end of the
     element's content. In valid documents, this would be the end tag for
     the element.
   * ID and NAME tokens must begin with a letter ([A-Za-z]) and may be
     followed by any number of letters, digits ([0-9]), hyphens ("-"),
     underscores ("_"), colons (":"), and periods (".").
   * IDREF and IDREFS are references to ID tokens defined by other
     attributes. IDREF is a single token and IDREFS is a space-separated
     list of tokens.
   * NUMBER tokens must contain at least one digit ([0-9]).

6.3 Text strings

A number of attributes ( %Text; in the DTD) take text that is meant to be
"human readable". For introductory about attributes, please consult the
tutorial discussion of attributes.

6.4 URIs

This specification uses the term URI as defined in [URI] (see also
[RFC1630]).

Note that URIs include URLs (as defined in [RFC1738] and [RFC1808]).

Relative URIs are resolved to full URIs using a base URI. [RFC1808], section
3, defines the normative algorithm for this process. For more information
about base URIs, please consult the section on base URIs in the chapter on
links.

URIs are represented in the DTD by the parameter entity %URI;.

URIs in general are case-sensitive. There may be URIs, or parts of URIs,
where case doesn't matter (e.g., machine names), but identifying these may
not be easy. Users should always consider that URIs are case-sensitive (to
be on the safe side).

Please consult the appendix for information about non-ASCII characters in
URI attribute values.

6.5 Colors

The attribute value type "color" (%Color;) refers to color definitions as
specified in [SRGB]. A color value may either be a hexadecimal number
(prefixed by a hash mark) or one of the following sixteen color names. The
color names are case-insensitive.

                         Color names and sRGB values

             Black = "#000000"              Green = "#008000"

             Silver = "#C0C0C0"             Lime = "#00FF00"

             Gray = "#808080"               Olive = "#808000"

             White = "#FFFFFF"              Yellow = "#FFFF00"

             Maroon = "#800000"             Navy = "#000080"

             Red = "#FF0000"                Blue = "#0000FF"

             Purple = "#800080"             Teal = "#008080"

             Fuchsia = "#FF00FF"            Aqua = "#00FFFF"

Thus, the color values "#800080" and "Purple" both refer to the color
purple.

6.5.1 Notes on using colors

Although colors can add significant amounts of information to document and
make them more readable, please consider the following guidelines when
including color in your documents:

   * The use of HTML elements and attributes for specifying color is
     deprecated. You are encouraged to use style sheets instead.
   * Don't use color combinations that cause problems for people with color
     blindness in its various forms.
   * If you use a background image or set the background color, then be sure
     to set the various text colors as well.
   * Colors specified with the BODY and FONT elements and bgcolor on tables
     look different on different platforms (e.g., workstations, Macs,
     Windows, and LCD panels vs. CRTs), so you shouldn't rely entirely on a
     specific effect. In the future, support for the [SRGB] color model
     together with ICC color profiles should mitigate this problem.
   * When practical, adopt common conventions to minimize user confusion.

6.6 Lengths

HTML specifies three types of length values for attributes:

  1. Pixels: The value ( %Pixels; in the DTD) is integer that represents the
     number of pixels of the canvas (screen, paper). Thus, the value "50"
     means fifty pixels. For normative information about the definition of a
     pixel, please consult [CSS1].
  2. Length: The value ( %Length; in the DTD) may be either a %Pixel; or a
     percentage of the available horizontal or vertical space. Thus, the
     value "50%" means half of the available space.
  3. MultiLength: The value ( %MultiLength; in the DTD) may be a %Length; or
     a relative length. A relative length has the form "i*", where "i" is an
     integer. When allotting space among elements competing for that space,
     user agents allot pixel and percentage lengths first, then divide up
     remaining available space among relative lengths. Each relative length
     receives a portion of the available space that is proportional to the
     integer preceding the "*". The value "*" is equivalent to "1*". Thus,
     if 60 pixels of space are available after the user agent allots pixel
     and percentage space, and the competing relative lengths are 1*, 2*,
     and 3*, the 1* will be alloted 10 pixels, the 2* will be alloted 20
     pixels, and the 3* will be alloted 30 pixels.

Length values are case-neutral.

6.7 Content types (MIME types)

Note. A "media type" (defined in [RFC2045] and [RFC2046]) specifies the
nature of a linked resource. This specification employs the term "content
type" rather than "media type" in accordance with current usage.
Furthermore, in this specification, "media type" may refer to the media
where a user agent renders a document.

This type is represented in the DTD by %ContentType;.

Content types are case-insensitive.

Examples of content types include "text/html", "image/png", "image/gif",
"video/mpeg", "audio/basic", "text/tcl", "text/javascript", and
"text/vbscript". For the current list of registered MIME types, please
consult [MIMETYPES].

Note. The content type "text/css", while not currently registered with IANA,
should be used when the linked resource is a [CSS1] style sheet.

6.8 Language codes

The value of attributes whose type is a language code ( %LanguageCode in the
DTD) refers to a language code as specified by [RFC1766], section 2. For
information on specifying language codes in HTML, please consult the section
on language codes. Whitespace is not allowed within the language-code.

Language codes are case-insensitive.

6.9 Character encodings

The "charset" attributes (%Charset in the DTD) refer to a character encoding
as described in the section on character encodings. Values must be strings
(e.g., "euc-jp") from the IANA registry (see [CHARSETS] for a complete
list).

Names of character encodings are case-insensitive.

User agents must follow the steps set out in the section on specifying
character encodings in order to determine the character encoding of an
external resource.

6.10 Single characters

Certain attributes call for single character from the document character
set. These attributes take the %Character type in the DTD.

Single characters may be specified with character references (e.g.,
"&amp;").

6.11 Dates and times

[ISO8601] allows many options and variations in the representation of dates
and times. The current specification uses one of the formats described in
the profile [DATETIME] for its definition of legal date/time strings (
%Datetime in the DTD).

The format is:

  YYYY-MM-DDThh:mm:ssTZD

where:

     YYYY = four-digit year
     MM   = two-digit month (01=January, etc.)
     DD   = two-digit day of month (01 through 31)
     hh   = two digits of hour (00 through 23) (am/pm NOT allowed)
     mm   = two digits of minute (00 through 59)
     ss   = two digits of second (00 through 59)
     TZD  = time zone designator

The time zone designator is one of:

Z
     indicates UTC (Coordinated Universal Time). The "Z" must be upper case.
+hh:mm
     indicates that the time is a local time which is hh hours and mm
     minutes ahead of UTC.
-hh:mm
     indicates that the time is a local time which is hh hours and mm
     minutes behind UTC.

Exactly the components shown here must be present, with exactly this
punctuation. Note that the "T" appears literally in the string (it must be
upper case), to indicate the beginning of the time element, as specified in
[ISO8601]

If a generating application does not know the time to the second, it may use
the value "00" for the seconds (and minutes and hours if necessary).

Note. [DATETIME] does not address the issue of leap seconds.

6.12 Link types

Authors may use the following recognized link types, listed here with their
conventional interpretations. In the DTD, %LinkTypes refers to a
space-separated list of link types. White space characters are not permitted
within link types.

These link types are case-insensitive, i.e., "Alternate" has the same
meaning as "alternate".

User agents, search engines, etc. may interpret these link types in a
variety of ways. For example, user agents may provide access to linked
documents through a navigation bar.

Alternate
     Designates substitute versions for the document in which the link
     occurs. When used together with the lang attribute, it implies a
     translated version of the document. When used together with the media
     attribute, it implies a version designed for a different medium (or
     media).
Stylesheet
     Refers to an external style sheet. See the section on external style
     sheets for details. This is used together with the link type
     "Alternate" for user-selectable alternate style sheets.
Start
     Refers to the first document in a collection of documents. This link
     type tells search engines which document is considered by the author to
     be the starting point of the collection.
Next
     Refers to the next document in an linear sequence of documents. User
     agents may choose to preload the "next" document, to reduce the
     perceived load time.
Prev
     Refers to the previous document in an ordered series of documents. Some
     user agents also support the synonym "Previous".
Contents
     Refers to a document serving as a table of contents. Some user agents
     also support the synonym ToC (from "Table of Contents").
Index
     Refers to a document providing an index for the current document.
Glossary
     Refers to a document providing a glossary of terms that pertain to the
     current document.
Copyright
     Refers to a copyright statement for the current document.
Chapter
     Refers to a document serving as a chapter in a collection of documents.
Section
     Refers to a document serving as a section in a collection of documents.
Subsection
     Refers to a document serving as a subsection in a collection of
     documents.
Appendix
     Refers to a document serving as an appendix in a collection of
     documents.
Help
     Refers to a document offering help (more information, links to other
     sources information, etc.)
Bookmark
     Refers to a bookmark. A bookmark is a link to a key entry point within
     an extended document. The title attribute may be used, for example, to
     label the bookmark. Note that several bookmarks may be defined in each
     document.

Authors may wish to define additional link types not described in this
specification. If they do so, they should use a profile to cite the
conventions used to define the link types. Please see the profile attribute
of the HEAD element for more details.

For further discussions about link types, please consult the section on
links in HTML documents.

6.13 Media descriptors

The following is a list of recognized media descriptors ( %MediaDesc in the
DTD).

screen
     Intended for non-paged computer screens.
tty
     Intended for media using a fixed-pitch character grid, such as
     teletypes, terminals, or portable devices with limited display
     capabilities.
tv
     Intended for television-type devices (low resolution, color, limited
     scrollability).
projection
     Intended for projectors.
handheld
     Intended for handheld devices (small screen, monochrome, bitmapped
     graphics, limited bandwidth).
print
     Intended for paged, opaque material and for documents viewed on screen
     in print preview mode.
braille
     Intended for braille tactile feedback devices.
aural
     Intended for speech synthesizers.
all
     Suitable for all devices.

Future versions of HTML may introduce new values and may allow parameterized
values. To facilitate the introduction of these extensions, conforming user
agents must be able to parse the media attribute value as follows:

  1. The value is a comma-separated list of entries. For example,

     media="screen, 3d-glasses, print and resolution > 90dpi"

     is mapped to:

     "screen"
     "3d-glasses"
     "print and resolution > 90dpi"

  2. Each entry is truncated just before the first character that isn't a US
     ASCII letter [a-zA-Z] (Unicode decimal 65-90, 97-122), digit [0-9]
     (Unicode hex 30-39), or hyphen (45). In the example, this gives:

     "screen"
     "3d-glasses"
     "print"

  3. A case-sensitive match is then made with the set of media types defined
     above. User agents may ignore entries that don't match. In the example
     we are left with screen and print.

Note. Style sheets may include media-dependent variations within them (e.g.,
the CSS @media construct). In such cases it may be appropriate to use
"media=all".

6.14 Script data

Script data ( %Script; in the DTD) can be the content of the SCRIPT element
and the value of intrinsic event attributes. User agents must not evaluate
script data as HTML markup but instead must pass it on as data to a script
engine.

The case-sensitivity of script data depends on the scripting language.

Please note that script data that is element content may not contain
character references, but script data that is the value of an attribute may
contain them. The appendix provides further information about specifying
non-HTML data.

6.15 Style sheet data

Style sheet data (%StyleSheet; in the DTD) can be the content of the STYLE
element and the value of the style attribute. User agents must not evaluate
style data as HTML markup.

The case-sensitivity of style data depends on the style sheet language.

Please note that style sheet data that is element content may not contain
character references, but style sheet data that is the value of an attribute
may contain them. The appendix provides further information about specifying
non-HTML data.

6.16 Frame target names

Except for the reserved names listed below, frame target names
(%FrameTarget; in the DTD) must begin with an alphabetic character (a-zA-Z).
User agents should ignore all other target names.

The following target names are reserved and have special meanings.

_blank
     The user agent should load the designated document in a new, unnamed
     window.
_self
     The user agent should load the document in the same frame as the
     element that refers to this target.
_parent
     The user agent should load the document into the immediate FRAMESET
     parent of the current frame. This value is equivalent to _self if the
     current frame has no parent.
_top
     The user agent should load the document into the full, original window
     (thus cancelling all other frames). This value is equivalent to _self
     if the current frame has no parent.

                 7 The global structure of an HTML document

Contents

  1. Introduction to the structure of an HTML document
  2. HTML version information
  3. The HTML element
  4. The document head
       1. HEAD element
       2. The TITLE element
       3. The title attribute
       4. Meta data
             + Specifying meta data
             + The META element
             + Meta data profiles
  5. The document body
       1. The BODY element
       2. Element identifiers: the id and class attributes
       3. Block-level and inline elements
       4. Grouping elements: the DIV and SPAN elements
       5. Headings: The H1, H2, H3, H4, H5, H6 elements
       6. The ADDRESS element

7.1 Introduction to the structure of an HTML document

An HTML 4.0 document is composed of three parts:

  1. a line containing HTML version information,
  2. a declarative header section (delimited by the HEAD element),
  3. a body, which contains the document's actual content. The body may be
     implemented by the BODY element or the FRAMESET element.

White space (spaces, newlines, tabs, and comments) may appear before or
after each section. Sections 2 and 3 should be delimited by the HTML
element.

Here's an example of a simple HTML document:

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0//EN"
   "http://www.w3.org/TR/REC-html40/strict.dtd">
<HTML>
   <HEAD>
      <TITLE>My first HTML document</TITLE>
   </HEAD>
   <BODY>
      <P>Hello world!
   </BODY>
</HTML>

7.2 HTML version information

A valid HTML document declares what version of HTML is used in the document.
The document type declaration names the document type definition (DTD) in
use for the document (see [ISO8879]).

HTML 4.0 specifies three DTDs, so authors must include one of the following
document type declarations in their documents. The DTDs vary in the elements
they support.

   * The HTML 4.0 Strict DTD includes all elements and attributes that have
     not been deprecated or do not appear in frameset documents. For
     documents that use this DTD, use this document type declaration:

     <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0//EN"
             "http://www.w3.org/TR/REC-html40/strict.dtd">

   * The HTML 4.0 Transitional DTD includes everything in the strict DTD
     plus deprecated elements and attributes (most of which concern visual
     presentation). For documents that use this DTD, use this document type
     declaration:

     <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"
             "http://www.w3.org/TR/REC-html40/loose.dtd">

   * The HTML 4.0 Frameset DTD includes everything in the transitional DTD
     plus frames as well. For documents that use this DTD, use this document
     type declaration:

     <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Frameset//EN"
             "http://www.w3.org/TR/REC-html40/frameset.dtd">

The URI in each document type declaration allows user agents to download the
DTD and any entity sets that are needed. The following URIs refer to DTDs
and entity sets for HTML 4.0 that W3C supports:

   * "http://www.w3.org/TR/REC-html40/strict.dtd" -- default strict DTD
   * "http://www.w3.org/TR/REC-html40/loose.dtd" -- loose DTD
   * "http://www.w3.org/TR/REC-html40/frameset.dtd" -- DTD for frameset
     documents
   * "http://www.w3.org/TR/REC-html40/HTMLlat1.ent" -- Latin-1 entities
   * "http://www.w3.org/TR/REC-html40/HTMLsymbol.ent" -- Symbol entities
   * "http://www.w3.org/TR/REC-html40/HTMLspecial.ent" -- Special entities

The binding between public identifiers and files can be specified using a
catalog file following the format recommended by the SGML Open Consortium
(see [SGMLOPEN]). A sample catalog file for HTML 4.0 is included at the
beginning of the section on SGML reference information for HTML. The last
two letters of the declaration indicate the language of the DTD. For HTML,
this is always English ("EN").

7.3 The HTML element

<!ENTITY % html.content "HEAD, BODY">

<!ELEMENT HTML O O (%html.content;)    -- document root element -->
<!ATTLIST HTML
  %i18n;                               -- lang, dir --
  >

Start tag: optional, End tag: optional

Attribute definitions

version = cdata [CN]
     Deprecated. The value of this attribute specifies which HTML DTD
     version governs the current document. This attribute has been
     deprecated because it is redundant with version information provided by
     the document type declaration.

Attributes defined elsewhere

   * lang (language information), dir (text direction)

After document type declaration, the remainder of an HTML document is
contained by the HTML element. Thus, a typical HTML document has this
structure:

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0//EN"
"http://www.w3.org/TR/REC-html40/strict.dtd">
<HTML>
...The head, body, etc. goes here...
</HTML>

7.4 The document head

7.4.1 HEAD element

<!-- %head.misc; defined earlier on as "SCRIPT|STYLE|META|LINK|OBJECT" -->
<!ENTITY % head.content "TITLE & BASE?">

<!ELEMENT HEAD O O (%head.content;) +(%head.misc;) -- document head -->
<!ATTLIST HEAD
  %i18n;                               -- lang, dir --
  profile     %URI;          #IMPLIED  -- named dictionary of meta info --
  >

Start tag: optional, End tag: optional

Attribute definitions

profile = uri [CT]
     This attribute specifies the location of one or more meta data
     profiles, separated by white space. For future extensions, user agents
     should consider the value to be a list even though this specification
     only considers the first URI to be significant. Profiles are discussed
     below in the section on meta data.

Attributes defined elsewhere

   * lang (language information), dir (text direction)

The HEAD element contains information about the current document, such as
its title, keywords that may be useful to search engines, and other data
that is not considered document content. User agents do not generally render
elements that appear in the HEAD as content. They may, however, make
information in the HEAD available to users through other mechanisms.

7.4.2 The TITLE element

<!-- The TITLE element is not considered part of the flow of text.
       It should be displayed, for example as the page header or
       window title. Exactly one title is required per document.
    -->
<!ELEMENT TITLE - - (#PCDATA) -(%head.misc;) -- document title -->
<!ATTLIST TITLE %i18n>

Start tag: required, End tag: required

Attributes defined elsewhere

   * lang (language information), dir (text direction)

Every HTML document must have a TITLE element in the HEAD section.

Authors should use the TITLE element to identify the contents of a document.
Since users often consult documents out of context, authors should provide
context-rich titles. Thus, instead of a title such as "Introduction", which
doesn't provide much contextual background, authors should supply a title
such as "Introduction to Medieval Bee-Keeping" instead.

For reasons of accessibility, user agents must always make the content of
the TITLE element available to users (including TITLE elements that occur in
frames). The mechanism for doing so depends on the user agent (e.g., as a
caption, spoken).

Titles may contain character entities (for accented characters, special
characters, etc.), but may not contain other markup. Here is a sample
document title:

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0//EN"
   "http://www.w3.org/TR/REC-html40/strict.dtd">
<HTML>
<HEAD>
<TITLE>A study of population dynamics</TITLE>
... other head elements...
</HEAD>
<BODY>
... document body...
</BODY>
</HTML>

7.4.3 The title attribute

Attribute definitions

title = text [CS]
     This attribute offers advisory information about the element for which
     it is set.

Unlike the TITLE element, which provides information about an entire
document and may only appear once, the title attribute may annotate any
number of elements. Please consult an element's definition to verify that it
supports this attribute.

Values of the title attribute may be rendered by user agents in a variety of
ways. For instance, visual browsers frequently display the title as a "tool
tip" (a short message that appears when the pointing device pauses over an
object). Audio user agents may speak the title information in a similar
context. For example, setting the attribute on a link allows user agents
(visual and non-visual) to tell users about the nature of the linked
resource:

...some text...
Here's a photo of
<A href="http://someplace.com/neatstuff.gif" title="Me scuba diving">
   me scuba diving last summer
</A>
...some more text...

The title attribute has an additional role when used with the LINK element
to designate an external style sheet. Please consult the section on links
and style sheets for details.

Note. To improve the quality of speech synthesis for cases handled poorly by
standard techniques, future versions of HTML may include an attribute for
encoding phonemic and prosodic information.

7.4.4 Meta data

As this specification is being written, work is underway that will allow
authors to assign richer machine-readable information about HTML documents
and other network-accessible resources. The W3C Resource Description
Language (see [RDF]) is being developed as a common framework for meta data.

HTML lets authors specify meta data -- information about a document rather
than document content -- in a variety of ways.

For example, to specify the author of a document, one may use the META
element as follows:

<META name="Author" content="Dave Raggett">

The META element specifies a property (here "Author") and assigns a value to
it (here "Dave Raggett").

This specification does not define a set of legal meta data properties. The
meaning of a property and the set of legal values for that property should
be defined in a reference lexicon called profile. For example, a profile
designed to help search engines index documents might define properties such
as "author", "copyright", "keywords", etc.

Specifying meta data

In general, specifying meta data involves two steps:

  1. Declaring a property and a value for that property. This may be done in
     two ways:
       1. From within a document, via the META element.
       2. From outside a document, by linking to meta data via the LINK
          element (see the section on link types).
  2. Referring to a profile where the property and its legal values are
     defined. To designate a profile, use the profile attribute of the HEAD
     element.

Note that since a profile is defined for the HEAD element, the same profile
applies to all META and LINK elements in the document head.

User agents are not required to support meta data mechanisms. For those that
choose to support meta data, this specification does not define how meta
data should be interpreted.

The META element

<!ELEMENT META - O EMPTY               -- generic metainformation -->
<!ATTLIST META
  %i18n;                               -- lang, dir, for use with content --
  http-equiv  NAME           #IMPLIED  -- HTTP response header name  --
  name        NAME           #IMPLIED  -- metainformation name --
  content     CDATA          #REQUIRED -- associated information --
  scheme      CDATA          #IMPLIED  -- select form of content --
  >

Start tag: required, End tag: forbidden

Attribute definitions

For the following attributes, the permitted values and their interpretation
are profile dependent:

name = name [CS]
     This attribute identifies a property name. This specification does not
     list legal values for this attribute.
content = cdata [CS]
     This attribute specifies a property's value. This specification does
     not list legal values for this attribute.
scheme = cdata [CS]
     This attribute names a scheme to be used to interpret the property's
     value (see the section on profiles for details).
http-equiv = name [CI]
     This attribute may be used in place of the name attribute. HTTP servers
     use this attribute to gather information for HTTP response message
     headers.

Attributes defined elsewhere

   * lang (language information), dir (text direction)

The META element can be used to identify properties of a document (e.g.,
author, expiration date, a list of key words, etc.) and assign values to
those properties. This specification does not define a normative set of
properties.

Each META element specifies a property/value pair. The name attribute
identifies the property and the content attribute specifies the property's
value.

For example, the following declaration sets a value for the Author property:

<META name="Author" content="Dave Raggett">

The lang attribute can be used with META to specify the language for the
value of the content attribute. This enables speech synthesizers to apply
language dependent pronunciation rules.

In this example, the author's name is declared to be French:

<META name="Author" lang="fr" content="Arnaud Le Hors">

Note. The META element is a generic mechanism for specifying meta data.
However, some HTML elements and attributes already handle certain pieces of
meta data and may be used by authors instead of META to specify those
pieces: the TITLE element, the ADDRESS element, the INS and DEL elements,
the title attribute, and the cite attribute.

Note. When a property specified by a META element takes a value that is a
URI, some authors prefer to specify the meta data via the LINK element.
Thus, the following meta data declaration:

<META name="DC.identifier"
      content="ftp://ds.internic.net/rfc/rfc1866.txt">

might also be written:

<LINK rel="DC.identifier"
         type="text/plain"
         href="ftp://ds.internic.net/rfc/rfc1866.txt">

META and HTTP headers

The http-equiv attribute can be used in place of the name attribute and has
a special significance when documents are retrieved via the Hypertext
Transfer Protocol (HTTP). HTTP servers may use the property name specified
by the http-equiv attribute to create an [RFC822]-style header in the HTTP
response. Please see the HTTP specification ([RFC2068]) for details on valid
HTTP headers.

The following sample META declaration:

<META http-equiv="Expires" content="Tue, 20 Aug 1996 14:25:27 GMT">

will result in the HTTP header:

Expires: Tue, 20 Aug 1996 14:25:27 GMT

This can be used by caches to determine when to fetch a fresh copy of the
associated document.

Some user agents support the use of META to refresh the current page after a
specified number of seconds, with the option of replacing it by a different
URI.

<META http-equiv="refresh" content="3,http://www.acme.com/intro.html">

The content is a number specifying the delay in seconds, followed by the URI
to load when the time is up. This mechanism is generally used to show users
a fleeting introductory page. However, since some user agents do not support
this mechanism, authors should include content on the introductory page to
allow users to navigate away from it (so they don't remain "stranded" on the
introductory page).

META and search engines

A common use for META is to specify keywords that a search engine may use to
improve the quality of search results. When several META elements provide
language-dependent information about a document, search engines may filter
on the lang attribute to display search results using the language
preferences of the user. For example,

<-- For speakers of US English -->
<META name="keywords" lang="en-us"
         content="vacation, Greece, sunshine">
<-- For speakers of British English -->
<META name="keywords" lang="en"
         content="holiday, Greece, sunshine">
<-- For speakers of French -->
<META name="keywords" lang="fr"
         content="vacances, Gr&egrave;ce, soleil">

The effectiveness of search engines can also be increased by using the LINK
element to specify links to translations of the document in other languages,
links to versions of the document in other media (e.g., PDF), and, when the
document is part of a collection, links to an appropriate starting point for
browsing the collection.

Further help is provided in the section on helping search engines index your
Web site.

META and PICS

The Platform for Internet Content Selection (PICS, specified in [PICS]) is
an infrastructure for associating labels (meta data) with Internet content.
Originally designed to help parents and teachers control what children can
access on the Internet, it also facilitates other uses for labels, including
code signing, privacy, and intellectual property rights management.

This example illustrates how one can use a META declaration to include a
PICS 1.1 label:

<HEAD>
 <META http-equiv="PICS-Label" content='
 (PICS-1.1 "http://www.gcf.org/v2.5"
    labels on "1994.11.05T08:15-0500"
      until "1995.12.31T23:59-0000"
      for "http://w3.org/PICS/Overview.html"
    ratings (suds 0.5 density 0 color/hue 1))
 '>
  <TITLE>... document title ...</TITLE>
</HEAD>

META and default information

The META element may be used to specify the default information for a
document in the following instances:

   * The default scripting language.
   * The default style sheet language.
   * The document character encoding.

The following example specifies the character encoding for a document as
being ISO-8859-5

<META http-equiv="Content-Type" content="text/html; charset=ISO-8859-5">

Meta data profiles

The profile attribute of the HEAD specifies the location of a meta data
profile. The value of the profile attribute is a URI. User agents may use
this URI in two ways:

   * As a globally unique name. User agents may be able to recognize the
     name (without actually retrieving the profile) and perform some
     activity based on known conventions for that profile. For instance,
     search engines could provide an interface for searching through
     catalogs of HTML documents, where these documents all use the same
     profile for representing catalog entries.
   * As a link. User agents may dereference the URI and, perform some
     activity based on the actual definitions within the profile (e.g.,
     authorize the usage of the profile within the current HTML document).
     This specification does not define formats for profiles.

This example refers to a hypothetical profile that defines useful properties
for document indexing. The properties defined by this profile -- including
"author", "copyright", "keywords", and "date" -- have their values set by
subsequent META declarations.

 <HEAD profile="http://www.acme.com/profiles/core">
  <TITLE>How to complete Memorandum cover sheets</TITLE>
  <META name="author" content="John Doe">
  <META name="copyright" content="&copy; 1997 Acme Corp.">
  <META name="keywords" content="corporate,guidelines,cataloging">
  <META name="date" content="1994-11-06T08:49:37+00:00">
 </HEAD>

As this specification is being written, it is common practice to use the
date formats described in [RFC2068], section 3.3. As these formats are
relatively hard to process, we recommend that authors use the [ISO8601] date
format. For more information, see the sections on the INS and DEL elements.

The scheme attribute allows authors to provide user agents more context for
the correct interpretation of meta data. At times, such additional
information may be critical, as when meta data may be specified in different
formats. For example, an author might specify a date in the (ambiguous)
format "10-9-97"; does this mean 9 October 1997 or 10 September 1997? The
scheme attribute value "Month-Date-Year" would disambiguate this date value.

At other times, the scheme attribute may provide helpful but non-critical
information to user agents.

For example, the following scheme declaration may help a user agent
determine that the value of the "identifier" property is an ISBN code
number:

<META scheme="ISBN"  name="identifier" content="0-8230-2355-9">

Values for the scheme attribute depend on the property name and the
associated profile.

Note. One sample profile is the Dublin Core (see [DCORE]). This profile
defines a set of recommended properties for electronic bibliographic
descriptions, and is intended to promote interoperability among disparate
description models.

7.5 The document body

7.5.1 The BODY element

<!ELEMENT BODY O O (%block;|SCRIPT)+ +(INS|DEL) -- document body -->
<!ATTLIST BODY
  %attrs;                              -- %coreattrs, %i18n, %events --
  onload          %Script;   #IMPLIED  -- the document has been loaded --
  onunload        %Script;   #IMPLIED  -- the document has been removed --
  >

Start tag: optional, End tag: optional

Attribute definitions

background = uri [CT]
     Deprecated.The value of this attribute is a URI that designates an
     image resource. The image generally tiles the background (for visual
     browsers).
text = color [CI]
     Deprecated.This attribute sets the foreground color for text (for
     visual browsers).
link = color [CI]
     Deprecated.This attribute sets the color of text marking unvisited
     hypertext links (for visual browsers).
vlink = color [CI]
     Deprecated.This attribute sets the color of text marking visited
     hypertext links (for visual browsers).
alink = color [CI]
     Deprecated.This attribute sets the color of text marking hypertext
     links when selected by the user (for visual browsers).

Attributes defined elsewhere

   * id, class (document-wide identifiers)
   * lang (language information), dir (text direction)
   * title (element title)
   * style (inline style information)
   * bgcolor (background color)
   * onload, onunload (intrinsic events)
   * onclick, ondblclick, onmousedown, onmouseup, onmouseover, onmousemove,
     onmouseout, onkeypress, onkeydown, onkeyup (intrinsic events)

The body of a document contains the document's content. The content may be
presented by a user agent in a variety of ways. For example, for visual
browsers, you can think of the body as a canvas where the content appears:
text, images, colors, graphics, etc. For audio user agents, the same content
may be spoken. Since style sheets are now the preferred way to specify a
document's presentation, the presentational attributes of BODY have been
deprecated.

DEPRECATED EXAMPLE:
The following HTML fragment illustrates the use of the deprecated
attributes. It sets the background color of the canvas to white, the text
foreground color to black, and the color of hyperlinks to red initially,
fuchsia when activated, and maroon once visited.

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"
   "http://www.w3.org/TR/REC-html40/loose.dtd">
<HTML>
<HEAD>
 <TITLE>A study of population dynamics</TITLE>
</HEAD>
<BODY bgcolor="white" text="black"
  link="red" alink="fuchsia" vlink="maroon">
  ... document body...
</BODY>
</HTML>

Using style sheets, the same effect could be accomplished as follows:

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0//EN"
   "http://www.w3.org/TR/REC-html40/strict.dtd">
<HTML>
<HEAD>
 <TITLE>A study of population dynamics</TITLE>
 <STYLE type="text/css">
  BODY { background: white; color: black}
  A:link { color: red }
  A:visited { color: maroon }
  A:active { color: fuchsia }
 </STYLE>
</HEAD>
<BODY>
  ... document body...
</BODY>
</HTML>

Using external (linked) style sheets gives you the flexibility to change the
presentation without revising the source HTML document:

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0//EN"
   "http://www.w3.org/TR/REC-html40/strict.dtd">
<HTML>
<HEAD>
 <TITLE>A study of population dynamics</TITLE>
 <LINK rel="stylesheet" type="text/css" href="smartstyle.css">
</HEAD>
<BODY>
  ... document body...
</BODY>
</HTML>

Framesets and HTML bodies. Documents that contain framesets replace the BODY
element by the FRAMESET element. Please consult the section on frames for
more information.

7.5.2 Element identifiers: the id and class attributes

Attribute definitions

id = name [CS]
     This attribute assigns a name to an element. This name must be unique
     in a document.
class = cdata-list [CS]
     This attribute assigns a class name or set of class names to an
     element. Any number of elements may be assigned the same class name or
     names. Multiple class names must be separated by white space
     characters.

The id attribute assigns a unique identifier to an element (which may be
verified by an SGML parser). For example, the following paragraphs are
distinguished by their id values:

<P id="myparagraph"> This is a uniquely named paragraph.</P>
<P id="yourparagraph"> This is also a uniquely named paragraph.</P>

The id attribute has several roles in HTML:

   * As a style sheet selector.
   * As a target anchor for hypertext links.
   * As a means to reference a particular element from a script.
   * As the name of a declared OBJECT element.
   * For general purpose processing by user agents (e.g. for identifying
     fields when extracting data from HTML pages into a database,
     translating HTML documents into other formats, etc.).

The class attribute, on the other hand, assigns one or more class names to
an element; the element may be said to belong to these classes. A class name
may be shared by several element instances. The class attribute has several
roles in HTML:

   * As a style sheet selector (when an author wishes to assign style
     information to a set of elements).
   * For general purpose processing by user agents.

In the following example, the SPAN element is used in conjunction with the
id and class attributes to markup document messages. Messages appear in both
English and French versions.

<!-- English messages -->
<P><SPAN id="msg1" class="info" lang="en">Variable declared twice</SPAN>
<P><SPAN id="msg2" class="warning" lang="en">Undeclared variable</SPAN>
<P><SPAN id="msg3" class="error" lang="en">Bad syntax for variable name</SPAN>

<!-- French messages -->
<P><SPAN id="msg1" class="info" lang="fr">Variable d&eacute;clar&eacute; deux fois</SPAN>
<P><SPAN id="msg2" class="warning" lang="fr">Variable ind&eacute;finie</SPAN>
<P><SPAN id="msg3" class="error" lang="fr">Erreur de syntaxe pour variable</SPAN>

The following CSS style rules would tell visual user agents to display
informational messages in green, warning messages in yellow, and error
messages in red:

SPAN.info    { color: green }
SPAN.warning { color: yellow }
SPAN.error   { color: red }

Note that the French "msg1" and the English "msg1" may not appear in the
same document since they share the same id value. Authors may make further
use of the id attribute to refine the presentation of individual messages,
make them target anchors, etc.

Almost every HTML element may be assigned identifier and class information.

Suppose, for example, that we are writing a document about a programming
language. The document is to include a number of preformatted examples. We
use the PRE element to format the examples. We also assign a background
color (green) to all instances of the PRE element belonging to the class
"example".

<HEAD>
<TITLE>... document title ...</TITLE>
<STYLE type="text/css">
PRE.example { background : green }
</STYLE>
</HEAD>
<BODY>
<PRE class="example" id="example-1">
...example code here...
</PRE>
</BODY>

By setting the id attribute for this example, we can (1) create a hyperlink
to it and (2) override class style information with instance style
information.

Note. The id attribute shares the same name space as the name attribute when
used for anchor names. Please consult the section on anchors with id for
more information.

7.5.3 Block-level and inline elements

Certain HTML elements that may appear in BODY are said to be "block-level"
while others are "inline" (also known as "text level"). The distinction is
founded on several notions:

Content model
     Generally, block-level elements may contain inline elements and other
     block-level elements. Generally, inline elements may contain only data
     and other inline elements. Inherent in this structural distinction is
     the idea that block elements create "larger" structures than inline
     elements.
Formatting
     By default, block-level elements are formatted differently than inline
     elements. Generally, block-level elements begin on new lines, inline
     elements do not. For information about white space, line breaks, and
     block formatting, please consult the section on text.
Directionality
     For technical reasons involving the [UNICODE] bidirectional text
     algorithm, block-level and inline elements differ in how they inherit
     directionality information. For details, see the section on inheritance
     of text direction.

Style sheets provide the means to specify the rendering of arbitrary
elements, including whether an element is rendered as block or inline. In
some cases, such as an inline style for list elements, this may be
appropriate, but generally speaking, authors are discouraged from overriding
the conventional interpretation of HTML elements in this way.

The alteration of the traditional presentation idioms for block level and
inline elements also has an impact on the bidirectional text algorithm. See
the section on the effect of style sheets on bidirectionality for more
information.

7.5.4 Grouping elements: the DIV and SPAN elements

<!ELEMENT DIV - - (%flow;)*            -- generic language/style container -->
<!ATTLIST DIV
  %attrs;                              -- %coreattrs, %i18n, %events --
  >
<!ELEMENT SPAN - - (%inline;)*         -- generic language/style container -->
<!ATTLIST SPAN
  %attrs;                              -- %coreattrs, %i18n, %events --
  >

Start tag: required, End tag: required

Attribute definitions

href = uri [CT]
     This attribute specifies a resource that provides more information
     about the content of the DIV or SPAN element.

Attributes defined elsewhere

   * id, class (document-wide identifiers)
   * lang (language information), dir (text direction)
   * title (element title)
   * style (inline style information)
   * align (alignment)
   * onclick, ondblclick, onmousedown, onmouseup, onmouseover, onmousemove,
     onmouseout, onkeypress, onkeydown, onkeyup (intrinsic events)

The DIV and SPAN elements, in conjunction with the id and class attributes,
offer a generic mechanism for adding structure to documents. These elements
define content to be inline (SPAN) or block-level (DIV) but impose no other
presentational idioms on the content. Thus, authors may use these elements
in conjunction with style sheets, the lang attribute, etc., to tailor HTML
to their own needs and tastes.

Suppose, for example, that we wanted to generate an HTML document based on a
database of client information. Since HTML does not include elements that
identify objects such as "client", "telephone number", "email address",
etc., we use DIV and SPAN to achieve the desired structural and
presentational effects. We might use the TABLE element as follows to
structure the information:

<!-- Example of data from the client database: -->
<!-- Name: Stephane Boyera, Tel: (212) 555-1212, Email: sb@foo.org -->

<DIV id="client-boyera" class="client">
<P><SPAN class="client-title">Client information:</SPAN>
<TABLE class="client-data">
<TR><TH>Last name:<TD>Boyera</TR>
<TR><TH>First name:<TD>Stephane</TR>
<TR><TH>Tel:<TD>(212) 555-1212</TR>
<TR><TH>Email:<TD>sb@foo.org</TR>
</TABLE>
</DIV>

<DIV id="client-lafon" class="client">
<P><SPAN class="client-title">Client information:</SPAN>
<TABLE class="client-data">
<TR><TH>Last name:<TD>Lafon</TR>
<TR><TH>First name:<TD>Yves</TR>
<TR><TH>Tel:<TD>(617) 555-1212</TR>
<TR><TH>Email:<TD>yves@coucou.com</TR>
</TABLE>
</DIV>

Later, we may easily add style sheet declaration to fine tune the
presentation of these database entries.

For another example of usage, please consult the example in the section on
the class and id attributes.

Visual user agents generally place a line break before and after DIV
elements, for instance:

<P>aaaaaaaaa<DIV>bbbbbbbbb</DIV><DIV>ccccc<P>ccccc</DIV>

which is typically rendered as:

aaaaaaaaa
bbbbbbbbb
ccccc

ccccc

7.5.5 Headings: The H1, H2, H3, H4, H5, H6 elements

<!ENTITY % heading "H1|H2|H3|H4|H5|H6">
<!--
  There are six levels of headings from H1 (the most important)
  to H6 (the least important).
-->

<!ELEMENT (%heading;)  - - (%inline;)* -- heading -->
<!ATTLIST (%heading;)
  %attrs;                              -- %coreattrs, %i18n, %events --
  >

Start tag: required, End tag: required

Attributes defined elsewhere

   * id, class (document-wide identifiers)
   * lang (language information), dir (text direction)
   * title (element title)
   * style (inline style information)
   * align (alignment)
   * onclick, ondblclick, onmousedown, onmouseup, onmouseover, onmousemove,
     onmouseout, onkeypress, onkeydown, onkeyup (intrinsic events)

A heading element briefly describes the topic of the section it introduces.
Heading information may be used by user agents, for example, to construct a
table of contents for a document automatically.

There are six levels of headings in HTML with H1 as the most important and
H6 as the least. Visual browsers usually render more important headings in
larger fonts than less important ones.

The following example shows how to use the DIV element to associate a
heading with the document section that follows it. Doing so allows you to
define a style for the section (color the background, set the font, etc.)
with style sheets.

<DIV class="section" id="forest-elephants" >
<H1>Forest elephants</H1>
<P>In this section, we discuss the lesser known forest elephants.
...this section continues...
<DIV class="subsection" id="forest-habitat" >
<H2>Habitat</H2>
<P>Forest elephants do not live in trees but among them.
...this subsection continues...
</DIV>
</DIV>

This structure may be decorated with style information such as:

<HEAD>
<TITLE>... document title ...</TITLE>
<STYLE type="text/css">
DIV.section { text-align: justify; font-size: 12pt}
DIV.subsection { text-indent: 2em }
H1 { font-style: italic; color: green }
H2 { color: green }
</STYLE>
</HEAD>

Numbered sections and references
HTML does not itself cause section numbers to be generated from headings.
This facility may be offered by user agents, however. Soon, style sheet
languages such as CSS will allow authors to control the generation of
section numbers (handy for forward references in printed documents, as in
"See section 7.2").

Some people consider skipping heading levels to be bad practice. They accept
H1 H2 H1 while they do not accept H1 H3 H1 since the heading level H2 is
skipped.

7.5.6 The ADDRESS element

<!ELEMENT ADDRESS - - (%inline;)* -- information on author -->
<!ATTLIST ADDRESS
  %attrs;                              -- %coreattrs, %i18n, %events --
  >

Start tag: required, End tag: required

Attributes defined elsewhere

   * id, class (document-wide identifiers)
   * lang (language information), dir (text direction)
   * onclick, ondblclick, onmousedown, onmouseup, onmouseover, onmousemove,
     onmouseout, onkeypress, onkeydown, onkeyup (intrinsic events)

The ADDRESS element may be used by authors to supply contact information for
document or a major part of a document such as a form. This element often
appears at the beginning or end of a document.

For example, a page at the W3C Web site related to HTML might include the
following contact information:

<ADDRESS>
<P><A href="../People/Raggett/">Dave Raggett</A>,
   <A href="../People/Arnaud/">Arnaud Le Hors</A>,
contact persons for the <A href="Activity">W3C HTML Activity</A><BR>
$Date: 1997/12/16 05:38:14 $
</ADDRESS>

                  8 Language information and text direction

Contents

  1. Specifying the language of content: the lang attribute
       1. Language codes
       2. Inheritance of language codes
       3. Interpretation of language codes
  2. Specifying the direction of text and tables: the dir attribute
       1. Introduction to the bidirectional algorithm
       2. Inheritance of text direction information
       3. Setting the direction of embedded text
       4. Overriding the bidirectional algorithm: the BDO element
       5. Character references for directionality and joining control
       6. The effect of style sheets on bidirectionality

This section of the document discusses two important issues that affect the
internationalization of HTML: specifying the language (the lang attribute)
and direction (the dir attribute) of text in a document.

8.1 Specifying the language of content: the lang attribute

Attribute definitions

lang = language-code [CI]
     This attribute specifies the base language of an element's attribute
     values and text content. The default value of this attribute is
     unknown.

Language information specified via the lang attribute may be used by a user
agent to control rendering in a variety of ways. Some situations where
author-supplied language information may be helpful include:

   * Assisting search engines
   * Assisting speech synthesizers
   * Helping a user agent select glyph variants for high quality typography
   * Helping a user agent choose a set of quotation marks
   * Helping a user agent make decisions about hyphenation, ligatures, and
     spacing
   * Assisting spell checkers and grammar checkers

The lang attribute specifies the language of element content and attribute
values; whether it is relevant for a given attribute depends on the syntax
and semantics of the attribute and the operation involved.

The intent of the lang attribute is to allow user agents to render content
more meaningfully based on accepted cultural practice for a given language.
This does not imply that user agents should render characters that are
atypical for a particular language in less meaningful ways; user agents must
make a best attempt to render all characters, regardless of the value
specified by lang.

For instance, if characters from the Greek alphabet appear in the midst of
English text:

<P><Q lang="en">"Her super-powers were the result of
&gamma;-radiation,</Q> he explained.</P>

a user agent (1) should try to render the English content in an appropriate
manner (e.g., in its handling the quotation marks) and (2) must make a best
attempt to render &gamma; even though it is not an English character.

Please consult the section on undisplayable characters for related
information.

8.1.1 Language codes

The lang attribute's value is a language code that identifies a natural
language spoken, written, or otherwise used for the communication of
information among people. Computer languages are explicitly excluded from
language codes.

[RFC1766] defines and explains the language codes that must be used in HTML
documents.

Briefly, language codes consist of a primary code and a possibly empty
series of subcodes:

        language-code = primary-code ( "-" subcode )*

Here are some sample language codes:

   * "en": English
   * "en-US": the U.S. version of English.
   * "en-cockney": the Cockney version of English.
   * "i-navajo": the Navajo language spoken by some Native Americans.
   * "x-klingon": The primary tag "x" indicates an experimental language tag

Two-letter primary codes are reserved for [ISO639] language abbreviations.
Two-letter codes include fr (French), de (German), it (Italian), nl (Dutch),
el (Greek), es (Spanish), pt (Portuguese), ar (Arabic), he (Hebrew), ru
(Russian), zh (Chinese), ja (Japanese), hi (Hindi), ur (Urdu), and sa
(Sanskrit).

Any two-letter subcode is understood to be a [ISO3166] country code.

8.1.2 Inheritance of language codes

An element inherits language code information according to the following
order of precedence (highest to lowest):

   * The lang attribute set for the element itself.
   * The closest parent element that has the lang attribute set (i.e., the
     lang attribute is inherited).
   * The HTTP "Content-Language" header (which may be configured in a
     server). For example:

     Content-Language: en-cockney

   * User agent default values and user preferences.

In this example, the primary language of the document is French ("fr"). One
paragraph is declared to be in Spanish ("es"), after which the primary
language returns to French. The following paragraph includes an embedded
Japanese ("ja") phrase, after which the primary language returns to French.

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0//EN"
   "http://www.w3.org/TR/REC-html40/strict.dtd">
<HTML lang="fr">
<HEAD>
<TITLE>Un document multilingue</TITLE>
</HEAD>
<BODY>
...Interpreted as French...
<P lang="es">...Interpreted as Spanish...
<P>...Interpreted as French again...
<P>...French text interrupted by<EM lang="ja">some
         Japanese</EM>French begins here again...
</BODY>
</HTML>

Note. Table cells may inherit lang values not from its parent but from the
first cell in a span. Please consult the section on alignment inheritance
for details.

8.1.3 Interpretation of language codes

In the context of HTML, a language code should be interpreted by user agents
as a hierarchy of tokens rather than a single token. When a user agent
adjusts rendering according to language information (say, by comparing style
sheet language codes and lang values), it should always favor an exact
match, but should also consider matching primary codes to be sufficient.
Thus, if the lang attribute value of "en-US" is set for the HTML element, a
user agent should prefer style information that matches "en-US" first, then
the more general value "en".

Note. Language code hierarchies do not guarantee that all languages with a
common prefix will be understood by those fluent in one or more of those
languages. They do allow a user to request this commonality when it is true
for that user.

8.2 Specifying the direction of text and tables: the dir attribute

Attribute definitions

dir = LTR | RTL [CI]
     This attribute specifies the base direction of directionally neutral
     text (i.e., text that doesn't have inherent directionality as defined
     in [UNICODE]) and the directionality of tables. Possible values:
        o LTR: Left-to-right text or table.
        o RTL: Right-to-left text or table.

In addition to specifying the language of a document with the lang
attribute, authors may need to specify the base directionality
(left-to-right or right-to-left) of portions of a document's text, of table
structure, etc. This is done with the dir attribute.

The [UNICODE] specification assigns directionality to characters and defines
a (complex) algorithm for determining the proper directionality of text. If
a document does not contain a displayable right-to-left character, a
conforming user agent is not required to apply the [UNICODE] bidirectional
algorithm. If a document contains right-to-left characters, and if the user
agent displays these characters, the user agent must use the bidirectional
algorithm.

Although Unicode specifies special characters that deal with text direction,
HTML offers higher-level markup constructs that do the same thing: the dir
attribute (do not confuse with the DIR element) and the BDO element. Thus,
to express a Hebrew quotation, it is more intuitive to write

<Q lang="he" dir="rtl">...a Hebrew quotation...</Q>

than the equivalent with Unicode references:

&#x202B;&#x05F4;...a Hebrew quotation...&#x05F4;&#x202C;

User agents must not use the lang attribute to determine text
directionality.

The dir attribute is inherited and may be overridden. Please consult the
section on the inheritance of text direction information for details.

8.2.1 Introduction to the bidirectional algorithm

The following example illustrates the expected behavior of the bidirectional
algorithm. It involves English, a left-to-right script, and Hebrew, a
right-to-left script.

Consider the following example text:

  english1 HEBREW2 english3 HEBREW4 english5 HEBREW6

The characters in this example (and in all related examples) are stored in
the computer the way they are displayed here: the first character in the
file is "e", the second is "n", and the last is "6".

Suppose the predominant language of the document containing this paragraph
is English. This means that the base direction is left-to-right. The correct
presentation of this line would be:

english1 2WERBEH english3 4WERBEH english5 6WERBEH
         <------          <------          <------
            H                H                H
------------------------------------------------->
                       E

The dotted lines indicate the structure of the sentence: English
predominates and some Hebrew text is embedded. Achieving the correct
presentation requires no additional markup since the Hebrew fragments are
reversed correctly by user agents applying the bidirectional algorithm.

If, on the other hand, the predominant language of the document is Hebrew,
the base direction is right-to-left. The correct presentation is therefore:

6WERBEH english5 4WERBEH english3 2WERBEH english1
        ------->         ------->         ------->
            E                E                E
<-------------------------------------------------
                       H

In this case, the whole sentence has been presented as right-to-left and the
embedded English sequences have been properly reversed by the bidirectional
algorithm.

8.2.2 Inheritance of text direction information

The Unicode bidirectional algorithm requires a base text direction for text
blocks. To specify the base direction of a block-level element, set the
element's dir attribute. The default value of the dir attribute is "ltr"
(left-to-right text).

When the dir attribute is set for a block-level element, it remains in
effect for the duration of the element and any nested block-level elements.
Setting the dir attribute on a nested element overrides the inherited value.

To set the base text direction for an entire document, set the dir attribute
on the HTML element.

For example:

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0//EN"
   "http://www.w3.org/TR/REC-html40/strict.dtd">
<HTML dir="RTL">
<HEAD>
<TITLE>...a right-to-left title...</TITLE>
</HEAD>
...right-to-left text...
<P dir="ltr">...left-to-right text...</P>
<P>...right-to-left text again...</P>
</HTML>

Inline elements, on the other hand, do not inherit the dir attribute. This
means that an inline element without a dir attribute does not open an
additional level of embedding with respect to the bidirectional algorithm.
(Here, an element is considered to be block-level or inline based on its
default presentation. Note that the INS and DEL elements can be block-level
or inline depending on their context.)

8.2.3 Setting the direction of embedded text

The [UNICODE] bidirectional algorithm automatically reverses embedded
character sequences according to their inherent directionality (as
illustrated by the previous examples). However, in general only one level of
embedding can be accounted for. To achieve additional levels of embedded
direction changes, you must make use of the dir attribute on an inline
element.

Consider the same example text as before:

english1 HEBREW2 english3 HEBREW4 english5 HEBREW6

Suppose the predominant language of the document containing this paragraph
is English. Furthermore, the above English sentence contains a Hebrew
section extending from HEBREW2 through HEBREW4 and the Hebrew section
contains an English quotation (english3). The desired presentation of the
text is thus:

english1 4WERBEH english3 2WERBEH english5 6WERBEH
                 ------->
                    E
         <-----------------------
                    H
------------------------------------------------->
                    E

To achieve two embedded direction changes, we must supply additional
information, which we do by delimiting the second embedding explicitly. In
this example, we use the SPAN element and the dir attribute to mark up the
text:

english1 <SPAN dir="RTL">HEBREW2 english3 HEBREW4</SPAN> english5 HEBREW6

Authors may also use special Unicode characters to achieve multiply embedded
direction changes. To achieve left-to-right embedding, surround embedded
text with the characters LEFT-TO-RIGHT EMBEDDING ("LRE", hexadecimal 202A)
and POP DIRECTIONAL FORMATTING ("PDF", hexadecimal 202C). To achieve
right-to-left embedding, surround embedded text with the characters
RIGHT-TO-LEFT EMBEDDING ("RTE", hexadecimal 202B) and PDF.

Using HTML directionality markup with Unicode characters. Authors and
designers of authoring software should be aware that conflicts can arise if
the dir attribute is used on inline elements (including BDO) concurrently
with the corresponding [UNICODE] formatting characters. Preferably one or
the other should be used exclusively. The markup method offers a better
guarantee of document structural integrity and alleviates some problems when
editing bidirectional HTML text with a simple text editor, but some software
may be more apt at using the [UNICODE] characters. If both methods are used,
great care should be exercised to insure proper nesting of markup and
directional embedding or override, otherwise, rendering results are
undefined.

8.2.4 Overriding the bidirectional algorithm: the BDO element

<!ELEMENT BDO - - (%inline;)*          -- I18N BiDi over-ride -->
<!ATTLIST BDO
  %coreattrs;                          -- id, class, style, title --
  lang        %LanguageCode; #IMPLIED  -- language code --
  dir         (ltr|rtl)      #REQUIRED -- directionality --
  >

Start tag: required, End tag: required

Attribute definitions

dir = LTR | RTL [CI]
     This mandatory attribute specifies the base direction of the element's
     text content. This direction overrides the inherent directionality of
     characters as defined in [UNICODE]. Possible values:
        o LTR: Left-to-right text.
        o RTL: Right-to-left text.

Attributes defined elsewhere

   * lang (language information)

The bidirectional algorithm and the dir attribute generally suffice to
manage embedded direction changes. However, some situations may arise when
the bidirectional algorithm results in incorrect presentation. The BDO
element allows authors to turn off the bidirectional algorithm for selected
fragments of text.

Consider a document containing the same text as before:

english1 HEBREW2 english3 HEBREW4 english5 HEBREW6

but assume that this text has already been put in visual order. One reason
for this may be that the MIME standard ([RFC2045], [RFC1556]) favors visual
order, i.e., that right-to-left character sequences are inserted
right-to-left in the byte stream. In an email, the above might be formatted,
including line breaks, as:

english1 2WERBEH english3
4WERBEH english5 6WERBEH

This conflicts with the [UNICODE] bidirectional algorithm, because that
algorithm would invert 2WERBEH, 4WERBEH, and 6WERBEH a second time,
displaying the Hebrew words left-to-right instead of right-to-left.

The solution in this case is to override the bidirectional algorithm by
putting the Email excerpt in a PRE element (to conserve line breaks) and
each line in a BDO element, whose dir attribute is set to LTR:

<PRE>
<BDO dir="LTR">english1 2WERBEH english3</BDO>
<BDO dir="LTR">4WERBEH english5 6WERBEH</BDO>
</PRE>

This tells the bidirectional algorithm "Leave me left-to-right!" and would
produce the desired presentation:

english1 2WERBEH english3
4WERBEH english5 6WERBEH

The BDO element should be used in scenarios where absolute control over
sequence order is required (e.g., multi-language part numbers). The dir
attribute is mandatory for this element.

Authors may also use special Unicode characters to override the
bidirectional algorithm -- LEFT-TO-RIGHT OVERRIDE (202D) or RIGHT-TO-LEFT
OVERRIDE (hexadecimal 202E). The POP DIRECTIONAL FORMATTING (hexadecimal
202C) character ends either bidirectional override.

Note. Recall that conflicts can arise if the dir attribute is used on inline
elements (including BDO) concurrently with the corresponding [UNICODE]
formatting characters.

Bidirectionality and character encoding According to [RFC1555] and
[RFC1556], there are special conventions for the use of "charset" parameter
values to indicate bidirectional treatment in MIME mail, in particular to
distinguish between visual, implicit, and explicit directionality. The
parameter value "ISO-8859-8" (for Hebrew) denotes visual encoding,
"ISO-8859-8-i" denotes implicit bidirectionality, and "ISO-8859-8-e" denotes
explicit directionality.

Because HTML uses the Unicode bidirectionality algorithm, conforming
documents encoded using ISO 8859-8 must be labeled as "ISO-8859-8-i".
Explicit directional control is also possible with HTML, but cannot be
expressed with ISO 8859-8, so "ISO-8859-8-e" should not be used.

The value "ISO-8859-8" implies that the document is formatted visually,
misusing some markup (such as TABLE with right alignment and no line
wrapping) to ensure reasonable display on older user agents that do not
handle bidirectionality. Such documents do not conform to the present
specification. If necessary, they can be made to conform to the current
specification (and at the same time will be displayed correctly on older
user agents) by adding BDO markup where necessary. Contrary to what is said
in [RFC1555] and [RFC1556], ISO-8859-6 (Arabic) is not visual ordering.

8.2.5 Character references for directionality and joining control

Since ambiguities sometimes arise as to the directionality of certain
characters (e.g., punctuation), the [UNICODE] specification includes
characters to enable their proper resolution. Also, Unicode includes some
characters to control joining behavior where this is necessary (e.g., some
situations with Arabic letters). HTML 4.0 includes character references for
these characters.

The following DTD excerpt presents some of the directional entities:

   <!ENTITY zwnj CDATA "&#8204;"--=zero width non-joiner-->
   <!ENTITY zwj  CDATA "&#8205;"--=zero width joiner-->
   <!ENTITY lrm  CDATA "&#8206;"--=left-to-right mark-->
   <!ENTITY rlm  CDATA "&#8207;"--=right-to-left mark-->

The zwnj entity is used to block joining behavior in contexts where joining
will occur but shouldn't. The zwj entity does the opposite; it forces
joining when it wouldn't occur but should. For example, the Arabic letter
"HEH" is used to abbreviate "Hijri", the name of the Islamic calendar
system. Since the isolated form of "HEH" looks like the digit five as
employed in Arabic script (based on Indic digits), in order to prevent
confusing "HEH" as a final digit five in a year, the initial form of "HEH"
is used. However, there is no following context (i.e., a joining letter) to
which the "HEH" can join. The zwj character provides that context.

Similarly, in Persian texts, there are cases where a letter that normally
would join a subsequent letter in a cursive connection should not. The
character zwnj is used to block joining in such cases.

The other characters, lrm and rlm, are used to force directionality of
directionally neutral characters. For example, if a double quotation mark
comes between an Arabic (right-to-left) and a Latin (left-to-right) letter,
the direction of the quotation mark is not clear (is it quoting the Arabic
text or the Latin text?). The lrm and rlm characters have a directional
property but no width and no word/line break property. Please consult
[UNICODE] for more details.

Mirrored character glyphs. In general, the bidirectional algorithm does not
mirror character glyphs but leaves them unaffected. An exception are
characters such as parentheses (see [UNICODE], table 4-7). In cases where
mirroring is desired, for example for Egyptian Hieroglyphs, Greek
Bustrophedon, or special design effects, this should be controlled with
styles.

8.2.6 The effect of style sheets on bidirectionality

In general, using style sheets to change an element's visual rendering from
block-level to inline or vice-versa is straightforward. However, because the
bidirectional algorithm relies on the inline/block-level distinction,
special care must be taken during the transformation.

When an inline element that does not have a dir attribute is transformed to
the style of a block-level element by a style sheet, it inherits the dir
attribute from its closest parent block element to define the base direction
of the block.

When a block element that does not have a dir attribute is transformed to
the style of an inline element by a style sheet, the resulting presentation
should be equivalent, in terms of bidirectional formatting, to the
formatting obtained by explicitly adding a dir attribute (assigned the
inherited value) to the transformed element.

                                   9 Text

Contents

  1. White space
  2. Structured text
       1. Phrase elements: EM, STRONG, DFN, CODE, SAMP, KBD, VAR, CITE,
          ABBR, and ACRONYM
       2. Quotations: The BLOCKQUOTE and Q elements
             + Rendering quotations
       3. Subscripts and superscripts: the SUB and SUP elements
  3. Lines and Paragraphs
       1. Paragraphs: the P element
       2. Controlling line breaks
             + Forcing a line break: the BR element
             + Prohibiting a line break
       3. Hyphenation
       4. Preformatted text: The PRE element
       5. Visual rendering of paragraphs
  4. Marking document changes: The INS and DEL elements

The following sections discuss issues surrounding the structuring of text.
Elements that present text (alignment elements, font elements, style sheets,
etc.) are discussed elsewhere in the specification. For information about
characters, please consult the section on the document character set.

9.1 White space

The document character set includes a wide variety of white space
characters. Many of these are typographic elements used in some applications
to produce particular visual spacing effects. In HTML, only the following
characters are defined as white space characters:

   * ASCII space (&#x0020;)
   * ASCII tab (&#x0009;)
   * ASCII form feed (&#x000C;)
   * Zero-width space (&#x200B;)

Line breaks are also white space characters. Note that although &#x2028; and
&#x2029; are defined in [ISO10646] to unambiguously separate lines and
paragraphs, respectively, these do not constitute line breaks in HTML, nor
does this specification include them in the more general category of white
space characters.

This specification does not indicate the behavior, rendering or otherwise,
of space characters other than those explicitly identified here as white
space characters. For this reason, authors should use appropriate elements
and styles to achieve visual formatting effects that involve white space,
rather than space characters.

For all HTML elements except PRE, sequences of white space separate "words"
(we use the term "word" here to mean "sequences of non-white space
characters"). When formatting text, user agents should identify these words
and lay them out according to the conventions of the particular written
language (script) and target medium.

This layout may involve putting space between words (called inter-word
space), but conventions for inter-word space vary from script to script. For
example, in Latin scripts, inter-word space is typically rendered as an
ASCII space (&#x0020;), while in Thai it is a zero-width word separator
(&#x200B;). In Japanese and Chinese, inter-word space is not typically
rendered at all.

Note that a sequence of white spaces between words in the source document
may result in an entirely different rendered inter-word spacing (except in
the case of the PRE element). In particular, user agents should collapse
input white space sequences when producing output inter-word space. This can
and should be done even in the absence of language information (from the
lang attribute, the HTTP "Content-Language" header field (see [RFC2068],
section 14.13), user agent settings, etc.).

The PRE element is used for preformatted text, where white space is
significant.

In order to avoid problems with SGML line break rules and inconsistencies
among extant implementations, authors should not rely on user agents to
render white space immediately after a start tag or immediately before an
end tag. Thus, authors, and in particular authoring tools, should write:

  <P>We offer free <A>technical support</A> for subscribers.</P>

and not:

  <P>We offer free<A> technical support </A>for subscribers.</P>

9.2 Structured text

9.2.1 Phrase elements: EM, STRONG, DFN, CODE, SAMP, KBD, VAR, CITE, ABBR,
and ACRONYM

<!ENTITY % phrase "EM | STRONG | DFN | CODE |
                   SAMP | KBD | VAR | CITE | ABBR | ACRONYM" >
<!ELEMENT (%fontstyle;|%phrase;) - - (%inline;)*>
<!ATTLIST (%fontstyle;|%phrase;)
  %attrs;                              -- %coreattrs, %i18n, %events --
  >

Start tag: required, End tag: required

Attributes defined elsewhere

   * id, class (document-wide identifiers)
   * lang (language information), dir (text direction)
   * title (element title)
   * style (inline style information )
   * onclick, ondblclick, onmousedown, onmouseup, onmouseover, onmousemove,
     onmouseout, onkeypress, onkeydown, onkeyup (intrinsic events )

Phrase elements add structural information to text fragments. The usual
meanings of phrase elements are following:

EM:
     Indicates emphasis.
STRONG:
     Indicates stronger emphasis.
CITE:
     Contains a citation or a reference to other sources.
DFN:
     Indicates that this is the defining instance of the enclosed term.
CODE:
     Designates a fragment of computer code.
SAMP:
     Designates sample output from programs, scripts, etc.
KBD:
     Indicates text to be entered by the user.
VAR:
     Indicates an instance of a variable or program argument.
ABBR:
     Indicates an abbreviated form (e.g., WWW, HTTP, URI, Mass., etc.).
ACRONYM:
     Indicates an acronym (e.g., WAC, radar, etc.).

EM and STRONG are used to indicate emphasis. The other phrase elements have
particular significance in technical documents. These examples illustrate
some of the phrase elements:

As <CITE>Harry S. Truman</CITE> said,
<Q lang="en-US">The buck stops here.</Q>

More information can be found in <CITE>[ISO-0000]</CITE>.

Please refer to the following reference number in future
correspondence: <STRONG>1-234-55</STRONG>

The presentation of phrase elements depends on the user agent. Generally,
visual user agents present EM text in italics and STRONG text in bold font.
Speech synthesizer user agents may change the synthesis parameters, such as
volume, pitch and rate accordingly.

The ABBR and ACRONYM elements allow authors to clearly indicate occurrences
of abbreviations and acronyms. Western languages make extensive use of
acronyms such as "GmbH", "NATO", and "F.B.I.", as well as abbreviations like
"M.", "Inc.", "et al.", "etc.". Both Chinese and Japanese use analogous
abbreviation mechanisms, wherein a long name is referred to subsequently
with a subset of the Han characters from the original occurrence. Marking up
these constructs provides useful information to user agents and tools such
as spell checkers, speech synthesizers, translation systems and
search-engine indexers.

The content of the ABBR and ACRONYM elements specifies the abbreviated
expression itself, as it would normally appear in running text. The title
attribute of these elements may be used to provide the full or expanded form
of the expression.

Here are some sample uses of ABBR:

  <P>
  <ABBR title="World Wide Web">WWW</ABBR>
  <ABBR lang="fr"
        title="Soci&eacute;t&eacute; Nationale des Chemins de Fer">
     SNCF
  </ABBR>
  <ABBR lang="es" title="Do&ntilde;a">Do&ntilde;a</ABBR>
  <ABBR title="Abbreviation">abbr.</ABBR>

Note that abbreviations and acronyms often have idiosyncratic
pronunciations. For example, while "IRS" and "BBC" are typically pronounced
letter by letter, "NATO" and "UNESCO" are pronounced phonetically. Still
other abbreviated forms (e.g., "URI" and "SQL") are spelled out by some
people and pronounced as words by other people. When necessary, authors
should use style sheets to specify the pronunciation of an abbreviated form.

9.2.2 Quotations: The BLOCKQUOTE and Q elements

<!ELEMENT BLOCKQUOTE - - (%block;|SCRIPT)+ -- long quotation -->
<!ATTLIST BLOCKQUOTE
  %attrs;                              -- %coreattrs, %i18n, %events --
  cite        %URI;          #IMPLIED  -- URI for source document or msg --
  >
<!ELEMENT Q - - (%inline;)*            -- short inline quotation -->
<!ATTLIST Q
  %attrs;                              -- %coreattrs, %i18n, %events --
  cite        %URI;          #IMPLIED  -- URI for source document or msg --
  >

Start tag: required, End tag: required

Attribute definitions

cite = uri [CT]
     The value of this attribute is a URI that designates a source document
     or message. This attribute is intended to give information about the
     source from which the quotation was borrowed.

Attributes defined elsewhere

   * id, class (document-wide identifiers)
   * lang (language information), dir (text direction)
   * title (element title)
   * style (inline style information )
   * onclick, ondblclick, onmousedown, onmouseup, onmouseover, onmousemove,
     onmouseout, onkeypress, onkeydown, onkeyup (intrinsic events )

These two elements designate quoted text. BLOCKQUOTE is for long quotations
(block-level content) and Q is intended for short quotations (inline
content) that don't require paragraph breaks.

This example formats an excerpt from "The Two Towers", by J.R.R. Tolkien, as
a blockquote.

<BLOCKQUOTE cite="http://www.mycom.com/tolkien/twotowers.html">
<P>They went in single file, running like hounds on a strong scent,
and an eager light was in their eyes. Nearly due west the broad
swath of the marching Orcs tramped its ugly slot; the sweet grass
of Rohan had been bruised and blackened as they passed.</P>
</BLOCKQUOTE>

Rendering quotations

Visual user agents generally render BLOCKQUOTE as an indented block.

Visual user agents must ensure that the content of the Q element is rendered
with delimiting quotation marks. Authors should not put quotation marks at
the beginning and end of the content of a Q element.

User agents should render quotation marks in a language-sensitive manner
(see the lang attribute). Many languages adopt different quotation styles
for outer and inner (nested) quotations, which should be respected by
user-agents.

The following example illustrates nested quotations with the Q element.

John said, <Q lang="en">I saw Lucy at lunch, she says
<Q lang="en">Mary wants you
to get some ice cream on your way home.</Q> I think I will get
some at Ben and Jerry's, on Gloucester Road.</Q>

Since the language of both quotations is English, user agents should render
them appropriately, for example with single quote marks around the inner
quotation and double quote marks around the outer quotation:

  John said, "I saw Lucy at lunch, she told me 'Mary wants you
  to get some ice cream on your way home.' I think I will get some
  at Ben and Jerry's, on Gloucester Road."

Note.We recommend that style sheet implementations provide a mechanism for
inserting quotation marks before and after a quotation delimited by
BLOCKQUOTE in a manner appropriate to the current language context and the
degree of nesting of quotations.

However, as some authors have used BLOCKQUOTE merely as a mechanism to
indent text, in order to preserve the intention of the authors, user agents
should not insert quotation marks in the default style.

The usage of BLOCKQUOTE to indent text is deprecated in favor of style
sheets.

9.2.3 Subscripts and superscripts: the SUB and SUP elements

<!ELEMENT (SUB|SUP) - - (%inline;)*    -- subscript, superscript -->
<!ATTLIST (SUB|SUP)
  %attrs;                              -- %coreattrs, %i18n, %events --
  >

Start tag: required, End tag: required

Attributes defined elsewhere

   * id, class (document-wide identifiers)
   * lang (language information), dir (text direction)
   * title (element title)
   * style (inline style information )
   * onclick, ondblclick, onmousedown, onmouseup, onmouseover, onmousemove,
     onmouseout, onkeypress, onkeydown, onkeyup (intrinsic events )

Many scripts (e.g., French) require superscripts or subscripts for proper
rendering. The SUB and SUP elements should be used to markup text in these
cases.

      H<sub>2</sub>O
      E = mc<sup>2</sup>
      <SPAN lang="fr">M<sup>lle</sup> Dupont</SPAN>

9.3 Lines and Paragraphs

Authors traditionally divide their thoughts and arguments into sequences of
paragraphs. The organization of information into paragraphs is not affected
by how the paragraphs are presented: paragraphs that are double-justified
contain the same thoughts as those that are left-justified.

The HTML markup for defining a paragraph is straightforward: the P element
defines a paragraph.

The visual presentation of paragraphs is not so simple. A number of issues,
both stylistic and technical, must be addressed:

   * Treatment of white space
   * Line breaking and word wrapping
   * Justification
   * Hyphenation
   * Written language conventions and text directionality
   * Formatting of paragraphs with respect to surrounding content

We address these questions below. Paragraph alignment and floating objects
are discussed later in this document.

9.3.1 Paragraphs: the P element

<!ELEMENT P - O (%inline;)*            -- paragraph -->
<!ATTLIST P
  %attrs;                              -- %coreattrs, %i18n, %events --
  >

Start tag: required, End tag: optional

Attributes defined elsewhere

   * id, class (document-wide identifiers)
   * lang (language information), dir (text direction)
   * title (element title)
   * style (inline style information )
   * align (alignment)
   * onclick, ondblclick, onmousedown, onmouseup, onmouseover, onmousemove,
     onmouseout, onkeypress, onkeydown, onkeyup (intrinsic events )

The P element represents a paragraph. It cannot contain block-level elements
(including P itself).

We discourage authors from using empty P elements. User agents should ignore
empty P elements.

9.3.2 Controlling line breaks

A line break is defined to be a carriage return (&#x000D;), a line feed
(&#x00OA;), or a carriage return/line feed pair. All line breaks constitute
white space.

For more information about SGML's specification of line breaks, please
consult the notes on line breaks in the appendix.

Forcing a line break: the BR element

<!ELEMENT BR - O EMPTY                 -- forced line break -->
<!ATTLIST BR
  %coreattrs;                          -- id, class, style, title --
  >

Start tag: required, End tag: forbidden

Attributes defined elsewhere

   * id, class (document-wide identifiers)
   * title (element title)
   * style (inline style information )
   * clear (alignment and floating objects )

The BR element forcibly breaks (ends) the current line of text.

For visual user agents, the clear attribute can be used to determine whether
markup following the BR element flows around images and other objects
floated to the left or right margin, or whether it starts after the bottom
of such objects. Further details are given in the section on alignment and
floating objects. Authors are advised to use style sheets to control text
flow around floating images and other objects.

With respect to bidirectional formatting, the BR element should behave the
same way the [ISO10646] LINE SEPARATOR character behaves in the
bidirectional algorithm.

Prohibiting a line break

Sometimes authors may want to prevent a line break from occurring between
two words. The &nbsp; entity (&#160; or &#xA0;) acts as a space where user
agents should not cause a line break.

9.3.3 Hyphenation

In HTML, there are two types of hyphens: the plain hyphen and the soft
hyphen. The plain hyphen should be interpreted by a user agent as just
another character. The soft hyphen tells the user agent where a line break
can occur.

Those browsers that interpret soft hyphens must observe the following
semantics: If a line is broken at a soft hyphen, a hyphen character must be
displayed at the end of the first line. If a line is not broken at a soft
hyphen, the user agent must not display a hyphen character. For operations
such as searching and sorting, the soft hyphen should always be ignored.

In HTML, the plain hyphen is represented by the "-" character (&#45; or
&#x2D;). The soft hyphen is represented by the character entity reference
&shy; (&#173; or &#xAD;)

9.3.4 Preformatted text: The PRE element

<!ENTITY % pre.exclusion "IMG|OBJECT|BIG|SMALL|SUB|SUP">

<!ELEMENT PRE - - (%inline;)* -(%pre.exclusion;) -- preformatted text -->
<!ATTLIST PRE
  %attrs;                              -- %coreattrs, %i18n, %events --
  >

Start tag: required, End tag: required

Attribute definitions

width = number [CN]
     This attribute provides a hint to visual user agents about the desired
     width of the formatted block. The user agent can use this information
     to select an appropriate font size or to indent the content
     appropriately. The desired width is expressed in number of characters.
     This attribute is not widely supported currently.

Attributes defined elsewhere

   * id, class (document-wide identifiers)
   * lang (language information), dir (text direction)
   * title (element title)
   * style (inline style information )
   * onclick, ondblclick, onmousedown, onmouseup, onmouseover, onmousemove,
     onmouseout, onkeypress, onkeydown, onkeyup (intrinsic events )

The PRE element tells visual user agents that the enclosed text is
"preformatted". When handling preformatted text, visual user agents:

   * May leave white space intact.
   * May render text with a fixed-pitch font.
   * May disable automatic word wrap.
   * Must not disable bidirectional processing.

Non-visual user agents are not required to respect extra white space in the
content of a PRE element.

For more information about SGML's specification of line breaks, please
consult the notes on line breaks in the appendix.

The DTD fragment above indicates which elements may not appear within a PRE
declaration. This is the same as in HTML 3.2, and is intended to preserve
constant line spacing and column alignment for text rendered in a fixed
pitch font. Authors are discouraged from altering this behavior through
style sheets.

The following example shows a preformatted verse from Shelly's poem To a
Skylark:

<PRE>
       Higher still and higher
         From the earth thou springest
       Like a cloud of fire;
         The blue deep thou wingest,
And singing still dost soar, and soaring ever singest.
</PRE>

Here is how this is typically rendered:

       Higher still and higher
         From the earth thou springest
       Like a cloud of fire;
         The blue deep thou wingest,
And singing still dost soar, and soaring ever singest.

The horizontal tab character
The horizontal tab character (decimal 9 in [ISO10646] and [ISO88591] ) is
usually interpreted by visual user agents as the smallest non-zero number of
spaces necessary to line characters up along tab stops that are every 8
characters. We strongly discourage using horizontal tabs in preformatted
text since it is common practice, when editing, to set the tab-spacing to
other values, leading to misaligned documents.

9.3.5 Visual rendering of paragraphs

Note.The following section is an informative description of the behavior of
some current visual user agents when formatting paragraphs. Style sheets
allow better control of paragraph formatting.

How paragraphs are rendered visually depends on the user agent. Paragraphs
are usually rendered flush left with a ragged right margin. Other defaults
are appropriate for right-to-left scripts.

HTML user agents have traditionally rendered paragraphs with white space
before and after, e.g.,

  At the same time, there began to take form a system of numbering,
  the calendar, hieroglyphic writing, and a technically advanced
  art, all of which later influenced other peoples.

  Within the framework of this gradual evolution or cultural
  progress the Preclassic horizon has been divided into Lower,
  Middle and Upper periods, to which can be added a transitional
  or Protoclassic period with several features that would later
  distinguish the emerging civilizations of Mesoamerica.

This contrasts with the style used in novels which indents the first line of
the paragraph and uses the regular line spacing between the final line of
the current paragraph and the first line of the next, e.g.,

     At the same time, there began to take form a system of
  numbering, the calendar, hieroglyphic writing, and a technically
  advanced art, all of which later influenced other peoples.
     Within the framework of this gradual evolution or cultural
  progress the Preclassic horizon has been divided into Lower,
  Middle and Upper periods, to which can be added a transitional
  or Protoclassic period with several features that would later
  distinguish the emerging civilizations of Mesoamerica.

Following the precedent set by the NCSA Mosaic browser in 1993, user agents
generally don't justify both margins, in part because it's hard to do this
effectively without sophisticated hyphenation routines. The advent of style
sheets, and anti-aliased fonts with subpixel positioning promises to offer
richer choices to HTML authors than previously possible.

Style sheets provide rich control over the size and style of a font, the
margins, space before and after a paragraph, the first line indent,
justification and many other details. The user agent's default style sheet
renders P elements in a familiar form, as illustrated above. One could, in
principle, override this to render paragraphs without the breaks that
conventionally distinguish successive paragraphs. In general, since this may
confuse readers, we discourage this practice.

By convention, visual HTML user agents wrap text lines to fit within the
available margins. Wrapping algorithms depend on the script being formatted.

In Western scripts, for example, text should only be wrapped at white space.
Early user agents incorrectly wrapped lines just after the start tag or just
before the end tag of an element, which resulted in dangling punctuation.
For example, consider this sentence:

   A statue of the <a href="cih78">Cihuateteus</a>, who are patron ...

Wrapping the line just before the end tag of the A element causes the comma
to be stranded at the beginning of the next line:

  A statue of the Cihuateteus
  , who are patron ...

This is an error since there was no white space at that point in the markup.

9.4 Marking document changes: The INS and DEL elements

<!-- INS/DEL are handled by inclusion on BODY -->
<!ELEMENT (INS|DEL) - - (%flow;)*      -- inserted text, deleted text -->
<!ATTLIST (INS|DEL)
  %attrs;                              -- %coreattrs, %i18n, %events --
  cite        %URI;          #IMPLIED  -- info on reason for change --
  datetime    %Datetime;     #IMPLIED  -- date and time of change --
  >

Start tag: required, End tag: required

Attribute definitions

cite = uri [CT]
     The value of this attribute is a URI that designates a source document
     or message. This attribute is intended to point to information
     explaining why a document was changed.
datetime = datetime [CS]
     The value of this attribute specifies the date and time when the change
     was made.

Attributes defined elsewhere

   * id, class (document-wide identifiers)
   * lang (language information), dir (text direction)
   * title (element title)
   * style (inline style information )
   * onclick, ondblclick, onmousedown, onmouseup, onmouseover, onmousemove,
     onmouseout, onkeypress, onkeydown, onkeyup (intrinsic events )

INS and DEL are used to markup sections of the document that have been
inserted or deleted with respect to a different version of a document (e.g.,
in draft legislation where lawmakers need to view the changes).

These two elements are unusual for HTML in that they may serve as either
block-level or inline elements (but not both). They may contain one or more
words within a paragraph or contain one or more block-level elements such as
paragraphs, lists and tables.

This example could be from a bill to change the legislation for how many
deputies a County Sheriff can employ from 3 to 5.

<P>
  A Sheriff can employ <DEL>3</DEL><INS>5</INS> deputies.
</P>

The INS and DEL elements must not contain block-level content when these
elements behave as inline elements.

ILLEGAL EXAMPLE:
The following is not legal HTML.

<P>
<INS><DIV>...block-level content...</DIV></INS>
</P>

User agents should render inserted and deleted text in ways that make the
change obvious. For instance, inserted text may appear in a special font,
deleted text may not be shown at all or be shown as struck-through or with
special markings, etc.

Both of the following examples correspond to November 5, 1994, 8:15:30 am,
US Eastern Standard Time.

     1994-11-05T13:15:30Z
     1994-11-05T08:15:30-05:00

Used with INS, this gives:

<INS datetime="1994-11-05T08:15:30-05:00"
        cite="http://www.foo.org/mydoc/comments.html">
Furthermore, the latest figures from the marketing department
suggest that such practice is on the rise.
</INS>

The document "http://www.foo.org/mydoc/comments.html" would contain comments
about why information was inserted into the document.

Authors may also make comments about inserted or deleted text by means of
the title attribute for the INS and DEL elements. User agents may present
this information to the user (e.g., as a popup note). For example:

<INS datetime="1994-11-05T08:15:30-05:00"
        title="Changed as a result of Steve B's comments in meeting.">
Furthermore, the latest figures from the marketing department
suggest that such practice is on the rise.
</INS>

                                  10 Lists

Contents

  1. Introduction to lists
  2. Unordered lists (UL), ordered lists (OL), and list items (LI)
  3. Definition lists: the DL, DT, and DD elements
       1. Visual rendering of lists
  4. The DIR and MENU elements

10.1 Introduction to lists

HTML offers authors several mechanisms for specifying lists of information.
All lists must contain one or more list elements. Lists may contain:

   * Unordered information.
   * Ordered information.
   * Definitions.

The previous list, for example, is an unordered list, created with the UL
element:

<UL>
<LI>Unordered information.
<LI>Ordered information.
<LI>Definitions.
</UL>

An ordered list, created using the OL element, should contain information
where order should be emphasized, as in a recipe:

  1. Mix dry ingredients thoroughly.
  2. Pour in wet ingredients.
  3. Mix for 10 minutes.
  4. Bake for one hour at 300 degrees.

Definition lists, created using the DL element, generally consist of a
series of term/definition pairs (although definition lists may have other
applications). Thus, when advertising a product, one might use a definition
list:

Lower cost
     The new version of this product costs significantly less than the
     previous one!
Easier to use
     We've changed the product so that it's much easier to use!
Safe for kids
     You can leave your kids alone in a room with this product and they
     won't get hurt (not a guarantee).

defined in HTML as:

<DL>
<DT><STRONG>Lower cost</STRONG>
<DD>The new version of this product costs significantly less than the
previous one!
<DT><STRONG>Easier to use</STRONG>
<DD>We've changed the product so that it's much easier to use!
<DT><STRONG>Safe for kids</STRONG>
<DD>You can leave your kids alone in a room with this product and
they won't get hurt (not a guarantee).
</DL>

Lists may also be nested and different list types may be used together, as
in the following example, which is a definition list that contains an
unordered list (the ingredients) and an ordered list (the procedure):

The ingredients:
        o 100 g. flour
        o 10 g. sugar
        o 1 cup water
        o 2 eggs
        o salt, pepper
The procedure:
       1. Mix dry ingredients thoroughly.
       2. Pour in wet ingredients.
       3. Mix for 10 minutes.
       4. Bake for one hour at 300 degrees.
Notes:
     The recipe may be improved by adding raisins.

The exact presentation of the three list types depends on the user agent. We
discourage authors from using lists purely as a means of indenting text.
This is a stylistic issue and is properly handled by style sheets.

10.2 Unordered lists (UL), ordered lists (OL), and list items (LI)

<!ELEMENT UL - - (LI)+                 -- unordered list -->
<!ATTLIST UL
  %attrs;                              -- %coreattrs, %i18n, %events --
  >
<!ELEMENT OL - - (LI)+                 -- ordered list -->
<!ATTLIST OL
  %attrs;                              -- %coreattrs, %i18n, %events --
  >

Start tag: required, End tag: required

<!ELEMENT LI - O (%flow;)*             -- list item -->
<!ATTLIST LI
  %attrs;                              -- %coreattrs, %i18n, %events --
  >

Start tag: required, End tag: optional

Attribute definitions

type =  style-information [CI]
     Deprecated. This attribute sets the style of a list item. Currently
     available values are intended for visual user agents. Possible values
     are described below (along with case information).
start = number [CN]
     Deprecated. For OL only. This attribute specifies the starting number
     of the first item in an ordered list. The default starting number is
     "1". Note that while the value of this attribute is an integer, the
     corresponding label may be non-numeric. Thus, when the list item style
     is upper case latin letters (A, B, C, ...), start=3 means "C". When the
     style is lower case roman numerals, start=3 means "iii", etc.
value = number [CN]
     Deprecated. For LI only. This attribute sets the number of the current
     list item. Note that while the value of this attribute is an integer,
     the corresponding label may be non-numeric (see the start attribute).
compact [CI]
     Deprecated. When set, this boolean attribute gives a hint to visual
     user agents to render the list in a more compact way. The
     interpretation of this attribute depends on the user agent.

Attributes defined elsewhere

   * id, class (document-wide identifiers)
   * lang (language information), dir (text direction)
   * title (element title)
   * style (inline style information)
   * onclick, ondblclick, onmousedown, onmouseup, onmouseover, onmousemove,
     onmouseout, onkeypress, onkeydown, onkeyup (intrinsic events)

Ordered and unordered lists are rendered in an identical manner except that
visual user agents number ordered list items. User agents may present those
numbers in a variety of ways. Unordered list items are not numbered.

Both types of lists are made up of sequences of list items defined by the LI
element (whose end tag may be omitted).

This example illustrates the basic structure of a list.

<UL>
   <LI> ... first list item...
   <LI> ... second list item...
   ...
</UL>

Lists may also be nested:

DEPRECATED EXAMPLE:

<UL>
     <LI> ... Level one, number one...
     <OL>
        <LI> ... Level two, number one...
        <LI> ... Level two, number two...
        <OL start="10">
           <LI> ... Level three, number one...
        </OL>
        <LI> ... Level two, number three...
     </OL>
     <LI> ... Level one, number two...
</UL>

Details about number order. In ordered lists, it is not possible to continue
list numbering automatically from a previous list or to hide numbering of
some list items. However, authors can reset the number of a list item by
setting its value attribute. Numbering continues from the new value for
subsequent list items. For example:

<ol>
<li value="30"> makes this list item number 30.
<li value="40"> makes this list item number 40.
<li> makes this list item number 41.
</ol>

10.3 Definition lists: the DL, DT, and DD elements

<!-- definition lists - DT for term, DD for its definition -->

<!ELEMENT DL - - (DT|DD)+              -- definition list -->
<!ATTLIST DL
  %attrs;                              -- %coreattrs, %i18n, %events --
  >

Start tag: required, End tag: required

<!ELEMENT DT - O (%inline;)*           -- definition term -->
<!ELEMENT DD - O (%flow;)*             -- definition description -->
<!ATTLIST (DT|DD)
  %attrs;                              -- %coreattrs, %i18n, %events --
  >

Start tag: required, End tag: optional

Attributes defined elsewhere

   * id, class (document-wide identifiers)
   * lang (language information), dir (text direction)
   * title (element title)
   * style (inline style information)
   * onclick, ondblclick, onmousedown, onmouseup, onmouseover, onmousemove,
     onmouseout, onkeypress, onkeydown, onkeyup (intrinsic events)

Definition lists vary only slightly from other types of lists in that list
items consist of two parts: a term and a description. The term is given by
the DT element and is restricted to inline content. The description is given
with a DD element that contains block-level content.

Here is an example:


<DL>
  <DT>Dweeb
  <DD>young excitable person who may mature
    into a <EM>Nerd</EM> or <EM>Geek</EM>

  <DT>Cracker
  <DD>hacker on the Internet

  <DT>Nerd
  <DD>male so into the Net that he forgets
    his wife's birthday
</DL>

Here is an example with multiple terms and descriptions:

<DL>
   <DT>Center
   <DT>Centre
   <DD> A point equidistant from all points
              on the surface of a sphere.
   <DD> In some field sports, the player who
              holds the middle position on the field, court,
              or forward line.
</DL>

Another application of DL, for example, is for marking up dialogues, with
each DT naming a speaker, and each DD containing his or her words.

10.3.1 Visual rendering of lists

Note.The following is an informative description of the behavior of some
current visual user agents when formatting lists. Style sheets allow better
control of list formatting (e.g., for numbering, language-dependent
conventions, indenting, etc.).

Visual user agents generally indent nested lists with respect to the current
level of nesting.

For both OL and UL, the type attribute specifies rendering options for
visual user agents.

For the UL element, possible values for the type attribute are disc, square,
and circle. The default value depends on the level of nesting of the current
list. These values are case-insensitive.

How each value is presented depends on the user agent. User agents should
attempt to present a "disc" as a small filled-in circle, a "circle" as a
small circle outline, and a "square" as a small square outline.

A graphical user agent might render this as:

[A possible rendering of a disc] for the value "disc"
[A possible rendering of a circle] for the value "circle"
[A possible rendering of a square] for the value "square"

For the OL element, possible values for the type attribute are summarized in
the table below (the are case-sensitive):

          Type                     Numbering style
           1          arabic numbers             1, 2, 3, ...
           a           lower alpha               a, b, c, ...
           A           upper alpha               A, B, C, ...
           i           lower roman             i, ii, iii, ...
           I           upper roman             I, II, III, ...

Note that the type attribute is deprecated and list styles should be handled
through style sheets.

For example, using CSS, one may specify that the style of numbers for list
elements in a numbered list should be lower case roman numerals. In the
excerpt below, every OL element belonging to the class "withroman" will have
roman numerals in front of its list items.

<STYLE type="text/css">
OL.withroman { list-style-type: lower-roman }
</STYLE>
<BODY>
<OL class="withroman">
<LI> Step one ...
<LI> Step two ...
</OL>
</BODY>

The rendering of a definition list also depends on the user agent. The
example:

<DL>
  <DT>Dweeb
  <DD>young excitable person who may mature
    into a <EM>Nerd</EM> or <EM>Geek</EM>

  <DT>Cracker
  <DD>hacker on the Internet

  <DT>Nerd
  <DD>male so into the Net that he forgets
    his wife's birthday
</DL>

might be rendered as follows:

Dweeb
       young excitable person who may mature into a Nerd or Geek
Cracker
       hacker on the Internet
Nerd
       male so into the Net that he forgets his wife's birthday

10.4 The DIR and MENU elements

DIR and MENU are deprecated.

See the Transitional DTD for the formal definition.

Attributes defined elsewhere

   * id, class (document-wide identifiers)
   * lang (language information), dir (text direction)
   * title (element title)
   * style (inline style information)
   * onclick, ondblclick, onmousedown, onmouseup, onmouseover, onmousemove,
     onmouseout, onkeypress, onkeydown, onkeyup (intrinsic events)

The DIR element was designed to be used for creating multicolumn directory
lists. The MENU element was designed to be used for single column menu
lists. Both elements have the same structure as UL, just different
rendering. In practice, a user agent will render a DIR or MENU list exactly
as a UL list.

We strongly recommend using UL instead of these elements.

                                  11 Tables

Contents

  1. Introduction to tables
  2. Elements for constructing tables
       1. The TABLE element
             + Table directionality
       2. Table Captions: The CAPTION element
       3. Row groups: the THEAD, TFOOT, and TBODY elements
       4. Column groups: the COLGROUP and COL elements
             + The COLGROUP element
             + The COL element
             + Calculating the number of columns in a table
             + Calculating the width of columns
       5. Table rows: The TR element
       6. Table cells: The TH and TD elements
             + Cells that span several rows or columns
  3. Table formatting by visual user agents
       1. Borders and rules
       2. Horizontal and vertical alignment
             + Inheritance of alignment specifications
       3. Cell margins
  4. Table rendering by non-visual user agents
       1. Associating header information with data cells
       2. Categorizing cells
       3. Algorithm to find heading information
  5. Sample table

11.1 Introduction to tables

The HTML table model allows authors to arrange data -- text, preformatted
text, images, links, forms, form fields, other tables, etc. -- into rows and
columns of cells.

Each table may have an associated caption (see the CAPTION element) that
provides a short description of the table's purpose. A longer description
may also be provided (via the summary attribute) for the benefit of people
using speech or Braille-based user agents.

Table rows may be grouped into a head, foot, and body sections, (via the
THEAD, TFOOT and TBODY elements, respectively). Row groups convey additional
structural information and may be rendered by user agents in ways that
emphasize this structure. User agents may exploit the head/body/foot
division to support scrolling of body sections independently of the head and
foot sections. When long tables are printed, the head and foot information
may be repeated on each page that contains table data.

Authors may also group columns to provide additional structural information
that may be exploited by user agents. Furthermore, authors may declare
column properties at the start of a table definition (via the COLGROUP and
COL elements) in a way that enables user agents to render the table
incrementally rather than having to wait for all the table data to arrive
before rendering.

Table cells may either contain "header" information (see the TH element) or
"data" (see the TD element). Cells may span multiple rows and columns. The
HTML 4.0 table model allows authors to label each cell so that non-visual
user agents may more easily communicate heading information about the cell
to the user. Not only do these mechanisms greatly assist users with visual
disabilities, they make it possible for multi-modal wireless browsers with
limited display capabilities (e.g., Web-enabled pagers and phones) to handle
tables.

Tables should not be used purely as a means to layout document content as
this may present problems when rendering to non-visual media. Additionally,
when used with graphics, these tables may force users to scroll horizontally
to view a table designed on a system with a larger display. To minimize
these problems, authors should use style sheets to control layout rather
than tables.

Note. This specification includes more detailed information about tables in
sections on table design rationale and implementation issues.

Here's a simple table that illustrates some of the features of the HTML
table model. The following table definition:

<TABLE border="1"
          summary="This table gives some statistics about fruit
                   flies: average height and weight, and percentage
                   with red eyes (for both males and females).">
<CAPTION><EM>A test table with merged cells</EM></CAPTION>
<TR><TH rowspan="2"><TH colspan="2">Average
    <TH rowspan="2">Red<BR>eyes
<TR><TH>height<TH>weight
<TR><TH>Males<TD>1.9<TD>0.003<TD>40%
<TR><TH>Females<TD>1.7<TD>0.002<TD>43%
</TABLE>

might be rendered something like this on a tty device:

          A test table with merged cells
    /-----------------------------------------\
    |          |      Average      |   Red    |
    |          |-------------------|  eyes    |
    |          |  height |  weight |          |
    |-----------------------------------------|
    |  Males   | 1.9     | 0.003   |   40%    |
    |-----------------------------------------|
    | Females  | 1.7     | 0.002   |   43%    |
    \-----------------------------------------/

or like this by a graphical user agent:

[A table with merged cells]

11.2 Elements for constructing tables

11.2.1 The TABLE element

<!ELEMENT TABLE - -
     (CAPTION?, (COL*|COLGROUP*), THEAD?, TFOOT?, TBODY+)>
<!ATTLIST TABLE                        -- table element --
  %attrs;                              -- %coreattrs, %i18n, %events --
  summary     %Text;         #IMPLIED  -- purpose/structure for speech output--
  width       %Length;       #IMPLIED  -- table width --
  border      %Pixels;       #IMPLIED  -- controls frame width around table --
  frame       %TFrame;       #IMPLIED  -- which parts of frame to render --
  rules       %TRules;       #IMPLIED  -- rulings between rows and cols --
  cellspacing %Length;       #IMPLIED  -- spacing between cells --
  cellpadding %Length;       #IMPLIED  -- spacing within cells --
  >

Start tag: required, End tag: required

Attribute definitions

summary = text [CS]
     This attribute provides a summary of the table's purpose and structure
     for user agents rendering to non-visual media such as speech and
     Braille.
align = left|center|right [CI]
     Deprecated. This attribute specifies the position of the table with
     respect to the document. Permitted values:
        o left: The table is to the left of the document.
        o center: The table is to the center of the document.
        o right: The table is to the right of the document.
width = length [CN]
     This attribute specifies the desired width of the entire table and is
     intended for visual user agents. When the value is a percentage value,
     the value is relative to the user agent's available horizontal space.
     In the absence of any width specification, table width is determined by
     the user agent.

Attributes defined elsewhere

   * id, class (document-wide identifiers)
   * lang (language information), dir (text direction)
   * title (element title)
   * style (inline style information )
   * onclick, ondblclick, onmousedown, onmouseup, onmouseover, onmousemove,
     onmouseout, onkeypress, onkeydown, onkeyup (intrinsic events)
   * bgcolor (background color)
   * frame, rules, border (borders and rules)
   * cellspacing, cellpadding (cell margins)

The TABLE element contains all other elements that specify caption, rows,
content, and formatting.

The following informative list describes what operations user agents may
carry out when rendering a table:

   * Make the table summary available to the user. Authors should provide a
     summary of a table's content and structure so that people using
     non-visual user agents may better understand it.
   * Render the caption, if one is defined.
   * Render the table header, if one is specified. Render the table footer,
     if one is specified. User agents must know where to render the header
     and footer. For instance, if the output medium is paged, user agents
     may put the header at the top of each page and the footer at the
     bottom. Similarly, if the user agent provides a mechanism to scroll the
     rows, the header may appear at the top of the scrolled area and the
     footer at the bottom.
   * Calculate the number of columns in the table. Note that the number of
     rows in a table is equal to the number of TR elements contained by the
     TABLE element.
   * Group the columns according to any column group specifications.
   * Render the cells, row by row and grouped in appropriate columns,
     between the header and footer. Visual user agents should format the
     table according to HTML attributes and style sheet specification.

The HTML table model has been designed so that, with author assistance, user
agents may render tables incrementally (i.e., as table rows arrive) rather
than having to wait for all the data before beginning to render.

In order for a user agent to format a table in one pass, authors must tell
the user agent:

   * The number of columns in the table. Please consult the section on
     calculating the number of columns in a table for details on how to
     supply this information.
   * The widths of these columns. Please consult the section on calculating
     the width of columns for details on how to supply this information.

More precisely, a user agent may render a table in a single pass when the
column widths are specified using a combination of COLGROUP and COL
elements. If any of the columns are specified in relative or percentage
terms (see the section on calculating the width of columns), authors must
also specify the width of the table itself.

Table directionality

The directionality of a table is either the inherited directionality (the
default is left-to-right) or that specified by the dir attribute for the
TABLE element.

For a left-to-right table, column zero is on the left side and row zero is
at the top. For a right-to-left table, column zero is on the right side and
row zero is at the top.

When a user agent allots extra cells to a row (see the section on
calculating the number of columns in a table), extra row cells are added to
the right of the table for left-to-right tables and to the left side for
right-to-left tables.

Note that TABLE is the only element on which dir reverses the visual order
of the columns; a single table row (TR) or a group of columns (COLGROUP)
cannot be independently reversed.

When set for the TABLE element, the dir attribute also affects the direction
of text within table cells (since the dir attribute is inherited by
block-level elements).

To specify a right-to-left table, set the dir attribute as follows:

<TABLE dir="RTL">
...the rest of the table...
</TABLE>

The direction of text in individual cells can be changed by setting the dir
attribute in an element that defines the cell. Please consult the section on
bidirectional text for more information on text direction issues.

11.2.2 Table Captions: The CAPTION element

<!ELEMENT CAPTION  - - (%inline;)*     -- table caption -->
<!ENTITY % CAlign "(top|bottom|left|right)">

<!ATTLIST CAPTION
  %attrs;                              -- %coreattrs, %i18n, %events --
  >

Start tag: required, End tag: required

Attribute definitions

align = top|bottom|left|right [CI]
     Deprecated. For visual user agents, this attribute specifies the
     position of the caption with respect to the table. Possible values:
        o top: The caption is at the top of the table. This is the default
          value.
        o bottom: The caption is at the bottom of the table.
        o left: The caption is at the left of the table.
        o right: The caption is at the right of the table.

Attributes defined elsewhere

   * id, class (document-wide identifiers)
   * lang (language information), dir (text direction)
   * title (element title)
   * style (inline style information )
   * onclick, ondblclick, onmousedown, onmouseup, onmouseover, onmousemove,
     onmouseout, onkeypress, onkeydown, onkeyup (intrinsic events )

When present, the CAPTION element's text should describe the nature of the
table. The CAPTION element is only permitted immediately after the TABLE
start tag. A TABLE element may only contain one CAPTION element.

Visual user agents allow sighted people to quickly grasp the structure of
the table from the headings as well as the caption. A consequence of this is
that captions will often be inadequate as a summary of the purpose and
structure of the table from the perspective of people relying on non-visual
user agents.

Authors should therefore take care to provide additional information
summarizing the purpose and structure of the table using the summary
attribute of the TABLE element. This is especially important for tables
without captions. Examples below illustrate the use of the summary
attribute.

Visual user agents should avoid clipping any part of the table including the
caption, unless a means is provided to access all parts, e.g., by horizontal
or vertical scrolling. We recommend that the caption text be wrapped to the
same width as the table. (See also the section on recommended layout
algorithms.)

11.2.3 Row groups: the THEAD, TFOOT, and TBODY elements

<!ELEMENT THEAD    - O (TR)+           -- table header -->
<!ELEMENT TFOOT    - O (TR)+           -- table footer -->

Start tag: required, End tag: optional

<!ELEMENT TBODY    O O (TR)+           -- table body -->

Start tag: optional, End tag: optional

<!ATTLIST (THEAD|TBODY|TFOOT)          -- table section --
  %attrs;                              -- %coreattrs, %i18n, %events --
  %cellhalign;                         -- horizontal alignment in cells --
  %cellvalign;                         -- vertical alignment in cells --
  >

Attributes defined elsewhere

   * id, class (document-wide identifiers)
   * lang (language information), dir (text direction)
   * title (element title)
   * style (inline style information )
   * onclick, ondblclick, onmousedown, onmouseup, onmouseover, onmousemove,
     onmouseout, onkeypress, onkeydown, onkeyup (intrinsic events )
   * align, char, charoff, valign (cell alignment)

Table rows may be grouped into a table head, table foot, and one or more
table body sections, using the THEAD, TFOOT and TBODY elements,
respectively. This division enables user agents to support scrolling of
table bodies independently of the table head and foot. When long tables are
printed, the table head and foot information may be repeated on each page
that contains table data.

The table head and table foot should contain information about the table's
columns. The table body should contain rows of table data.

When present, each THEAD, TFOOT, and TBODY contains a row group. Each row
group must contain at least one row, defined by the TR element.

This example illustrates the order and structure of table heads, feet, and
bodies.

<TABLE>
<THEAD>
     <TR> ...header information...
</THEAD>
<TFOOT>
     <TR> ...footer information...
</TFOOT>
<TBODY>
     <TR> ...first row of block one data...
     <TR> ...second row of block one data...
</TBODY>
<TBODY>
     <TR> ...first row of block two data...
     <TR> ...second row of block two data...
     <TR> ...third row of block two data...
</TBODY>
</TABLE>

TFOOT must appear before TBODY within a TABLE definition so that user agents
can render the foot before receiving all of the (potentially numerous) rows
of data. The following summarizes which tags are required and which may be
omitted:

   * The TBODY start tag is always required except when the table contains
     only one table body and no table head or foot sections. The TBODY end
     tag may always be safely omitted.
   * The start tags for THEAD and TFOOT are required when the table head and
     foot sections are present respectively, but the corresponding end tags
     may always be safely omitted.

Conforming user agent parsers must obey these rules for reasons of backward
compatibility.

The table of the previous example could be shortened by removing certain end
tags, as in:

<TABLE>
<THEAD>
     <TR> ...header information...
<TFOOT>
     <TR> ...footer information...
<TBODY>
     <TR> ...first row of block one data...
     <TR> ...second row of block one data...
<TBODY>
     <TR> ...first row of block two data...
     <TR> ...second row of block two data...
     <TR> ...third row of block two data...
</TABLE>

The THEAD, TFOOT, and TBODY sections must contain the same number of
columns.

11.2.4 Column groups: the COLGROUP and COL elements

Column groups allow authors to create structural divisions within a table.
Authors may highlight this structure through style sheets or HTML attributes
(e.g., the rules attribute for the TABLE element). For an example of the
visual presentation of column groups, please consult the sample table.

A table may either contain a single implicit column group (no COLGROUP
element delimits the columns) or any number of explicit column groups (each
delimited by an instance of the COLGROUP element).

The COL element allows authors to share attributes among several columns
without implying any structural grouping. The "span" of the COL element is
the number of columns that will share the element's attributes.

The COLGROUP element

<!ELEMENT COLGROUP - O (col)*          -- table column group -->
<!ATTLIST COLGROUP
  %attrs;                              -- %coreattrs, %i18n, %events --
  span        NUMBER         1         -- default number of columns in group --
  width       %MultiLength;  #IMPLIED  -- default width for enclosed COLs --
  %cellhalign;                         -- horizontal alignment in cells --
  %cellvalign;                         -- vertical alignment in cells --
  >

Start tag: required, End tag: optional

Attribute definitions

span = number [CN]
     This attribute, which must be an integer > 0, specifies the number of
     columns in a column group. Values mean the following:
        o In the absence of a span attribute, each COLGROUP defines a column
          group containing one column.
        o If the span attribute is set to N > 0, the current COLGROUP
          element defines a column group containing N columns.

     User agents must ignore this attribute if the COLGROUP element contains
     one or more COL elements.

width = multi-length [CN]

     This attribute specifies a default width for each column in the current
     column group. In addition to the standard pixel, percentage, and
     relative values, this attribute allows the special form "0*" (zero
     asterisk) which means that the width of the each column in the group
     should be the minimum width necessary to hold the column's contents.
     This implies that a column's entire contents must be known before its
     width may be correctly computed. Authors should be aware that
     specifying "0*" will prevent visual user agents from rendering a table
     incrementally.

     This attribute is overridden for any column in the column group whose
     width is specified via a COL element.

Attributes defined elsewhere

   * id, class (document-wide identifiers)
   * lang (language information), dir (text direction)
   * title (element title)
   * style (inline style information )
   * onclick, ondblclick, onmousedown, onmouseup, onmouseover, onmousemove,
     onmouseout, onkeypress, onkeydown, onkeyup (intrinsic events )
   * align, char, charoff, valign (cell alignment)

The COLGROUP element creates an explicit column group. The number of columns
in the column group may be specified in two, mutually exclusive ways:

  1. The element's span attribute (default value 1) specifies the number of
     columns in the group.
  2. Each COL element in the COLGROUP represents one or more columns in the
     group.

The advantage of using the span attribute is that authors may group together
information about column widths. Thus, if a table contains forty columns,
all of which have a width of 20 pixels, it is easier to write:

   <COLGROUP span="40" width="20">
   </COLGROUP>

than:

   <COLGROUP>
      <COL width="20">
      <COL width="20">
      ...a total of forty COL elements...
   </COLGROUP>

When it is necessary to single out a column (e.g., for style information, to
specify width information, etc.) within a group, authors must identify that
column with a COL element. Thus, to apply special style information to the
last column of the previous table, we single it out as follows:

   <COLGROUP width="20">
      <COL span="39">
      <COL id="format-me-specially">
   </COLGROUP>

The width attribute of the COLGROUP element is inherited by all 40 columns.
The first COL element refers to the first 39 columns (doing nothing special
to them) and the second one assigns an id value to the fortieth columns so
that style sheets may refer to it.

The table in the following example contains two column groups. The first
column group contains 10 columns and the second contains 5 columns. The
default width for each column in the first column group is 50 pixels. The
width of each column in the second column group will be the minimum required
for that column.

<TABLE>
<COLGROUP span="10" width="50">
<COLGROUP span="5" width="0*">
<THEAD>
<TR><TD> ...
</TABLE>

The COL element

<!ELEMENT COL      - O EMPTY           -- table column -->
<!ATTLIST COL                          -- column groups and properties --
  %attrs;                              -- %coreattrs, %i18n, %events --
  span        NUMBER         1         -- COL attributes affect N columns --
  width       %MultiLength;  #IMPLIED  -- column width specification --
  %cellhalign;                         -- horizontal alignment in cells --
  %cellvalign;                         -- vertical alignment in cells --
  >

Start tag: required, End tag: forbidden

Attribute definitions

span = number [CN]
     This attribute, whose value must be an integer > 0, specifies the
     number of columns "spanned" by the COL element; the COL element shares
     its attributes with all the columns it spans. The default value for
     this attribute is 1 (i.e., the COL element refers to a single column).
     If the span attribute is set to N > 1, the current COL element shares
     its attributes with the next N-1 columns.
width = multi-length [CN]
     This attribute specifies a default width for each column spanned by the
     current COL element. It has the same meaning as the width attribute for
     the COLGROUP element and overrides it.

Attributes defined elsewhere

   * id, class (document-wide identifiers)
   * lang (language information), dir (text direction)
   * title (element title)
   * style (inline style information )
   * onclick, ondblclick, onmousedown, onmouseup, onmouseover, onmousemove,
     onmouseout, onkeypress, onkeydown, onkeyup (intrinsic events )
   * align, char, charoff, valign (cell alignment)

The COL element allows authors to group together attribute specifications
for table columns. The COL does not group columns together structurally --
that is the role of the COLGROUP element. COL elements are empty and serve
only as a support for attributes. They may appear inside or outside an
explicit column group (i.e., COLGROUP element).

The width attribute for COL refers to the width of each column in the
element's span.

Calculating the number of columns in a table

There are two ways to determine the number of columns in a table (in order
of precedence):

  1. If the TABLE element contains any COLGROUP or COL elements, user agents
     should calculate the number of columns by summing the following:
        o For each COL element, take the value of its span attribute
          (default value 1).
        o For each COLGROUP element containing at least one COL element,
          ignore the span attribute for the COLGROUP element. For each COL
          element, perform the calculation of step 1.
        o For each empty COLGROUP element, take the value of its span
          attribute (default value 1).
  2. Otherwise, if the TABLE element contains no COLGROUP or COL elements,
     user agents should base the number of columns on what is required by
     the rows. The number of columns is equal to the number of columns
     required by the row with the most columns, including cells that span
     multiple columns. For any row that has fewer than this number of
     columns, the end of that row should be padded with empty cells. The
     "end" of a row depends on the table directionality.

It is an error if a table contains COLGROUP or COL elements and the two
calculations do not result in the same number of columns.

Once the user agent has calculated the number of columns in the table, it
may group them into column groups.

For example, for each of the following tables, the two column calculation
methods should result in three columns. The first three tables may be
rendered incrementally.

<TABLE>
<COLGROUP span="3"></COLGROUP>
<TR><TD> ...
...rows...
</TABLE>

<TABLE>
<COLGROUP>
<COL>
<COL span="2">
</COLGROUP>
<TR><TD> ...
...rows...
</TABLE>

<TABLE>
<COLGROUP>
<COL>
</COLGROUP>
<COLGROUP span="2">
<TR><TD> ...
...rows...
</TABLE>

<TABLE>
<TR>
  <TD><TD><TD>
</TR>
</TABLE>

Calculating the width of columns

Authors may specify column widths in three ways:

Fixed
     A fixed width specification is given in pixels (e.g., width="30"). A
     fixed-width specification enables incremental rendering.
Percentage
     A percentage specification (e.g., width="20%") is based on the
     percentage of the horizontal space available to the table (between the
     current left and right margins, including floats). Note that this space
     does not depend on the table itself, and thus percentage specifications
     enable incremental rendering.
Proportional
     Proportional specifications (e.g., width="3*") refer to portions of the
     horizontal space required by a table. If the table width is given a
     fixed value via the width attribute of the TABLE element, user agents
     may render the table incrementally even with proportional columns.

     However, if the table does not have a fixed width, user agents must
     receive all table data before they can determine the horizontal space
     required by the table. Only then may this space be allotted to
     proportional columns.

If an author specifies no width information for a column, a user agent may
not be able to incrementally format the table since it must wait for the
entire column of data to arrive in order to allot an appropriate width.

If column widths prove to be too narrow for the contents of a particular
table cell, user agents may choose to reflow the table.

The table in this example contains six columns. The first one does not
belong to an explicit column group. The next three belong to the first
explicit column group and the last two belong to the second explicit column
group. This table cannot be formatted incrementally since it contains
proportional column width specifications and no value for the width
attribute for the TABLE element.

Once the (visual) user agent has received the table's data: the available
horizontal space will be alloted by the user agent as follows: First the
user agent will allot 30 pixels to columns one and two. Then, the minimal
space required for the third column will be reserved. The remaining
horizontal space will be divided into six equal portions (since 2* + 1* + 3*
= 6 portions). Column four (2*) will receive two of these portions, column
five (1*) will receive one, and column six (3*) will receive three.


<TABLE>
<COLGROUP>
   <COL width="30">
<COLGROUP>
   <COL width="30">
   <COL width="0*">
   <COL width="2*">
<COLGROUP align="center">
   <COL width="1*">
   <COL width="3*" align="char" char=":">
<THEAD>
<TR><TD> ...
...rows...
</TABLE>

We have set the value of the align attribute in the second column group to
"center". All cells in every column in this group will inherit this value,
but may override it. In fact, the final COL does just that, by specifying
that every cell in the column it governs will be aligned along the ":"
character.

In the following table, the column width specifications allow the user agent
to format the table incrementally:


<TABLE width="200">
<COLGROUP span="10" width="15">
<COLGROUP width="*">
   <COL id="penultimate-column">
   <COL id="last-column">
<THEAD>
<TR><TD> ...
...rows...
</TABLE>

The first ten columns will be 15 pixels wide each. The last two columns will
each receive half of the remaining 50 pixels. Note that the COL elements
appear only so that an id value may be specified for the last two columns.

Note. Although the width attribute on the TABLE element is not deprecated,
authors are encouraged to use style sheets to specify table widths.

11.2.5 Table rows: The TR element

<!ELEMENT TR       - O (TH|TD)+        -- table row -->
<!ATTLIST TR                           -- table row --
  %attrs;                              -- %coreattrs, %i18n, %events --
  %cellhalign;                         -- horizontal alignment in cells --
  %cellvalign;                         -- vertical alignment in cells --
  >

Start tag: required, End tag: optional

Attributes defined elsewhere

   * id, class (document-wide identifiers)
   * lang (language information), dir (text direction)
   * title (element title)
   * style (inline style information )
   * onclick, ondblclick, onmousedown, onmouseup, onmouseover, onmousemove,
     onmouseout, onkeypress, onkeydown, onkeyup (intrinsic events )
   * align, char, charoff, valign (cell alignment)

The TR elements acts as a container for a row of table cells. The end tag
may be omitted.

This sample table contains three rows, each begun by the TR element:

<TABLE summary="This table charts the number of cups
                   of coffee consumed by each senator, the type
                   of coffee (decaf or regular), and whether
                   taken with sugar.">
<CAPTION>Cups of coffee consumed by each senator</CAPTION>
<TR> ...A header row...
<TR> ...First row of data...
<TR> ...Second row of data...
...the rest of the table...
</TABLE>

11.2.6 Table cells: The TH and TD elements

<!ELEMENT (TH|TD)  - O (%flow;)*       -- table header cell, table data cell-->

<!-- Scope is simpler than axes attribute for common tables -->
<!ENTITY % Scope "(row|col|rowgroup|colgroup)">

<!-- TH is for headers, TD for data, but for cells acting as both use TD -->
<!ATTLIST (TH|TD)                      -- header or data cell --
  %attrs;                              -- %coreattrs, %i18n, %events --
  abbr        %Text;         #IMPLIED  -- abbreviation for header cell --
  axis        CDATA          #IMPLIED  -- names groups of related headers--
  headers     IDREFS         #IMPLIED  -- list of id's for header cells --
  scope       %Scope;        #IMPLIED  -- scope covered by header cells --
  rowspan     NUMBER         1         -- number of rows spanned by cell --
  colspan     NUMBER         1         -- number of cols spanned by cell --
  %cellhalign;                         -- horizontal alignment in cells --
  %cellvalign;                         -- vertical alignment in cells --
  >

Start tag: required, End tag: optional

Attribute definitions

headers = idrefs [CS]
     This attribute specifies the list of header cells that provide header
     information for the current data cell. The value of this attribute is a
     space-separated list of cell names; those cells must be named by
     setting their id attribute. Authors generally use the headers attribute
     to help non-visual user agents render header information about data
     cells (e.g., header information is spoken prior to the cell data), but
     the attribute may also be used in conjunction with style sheets. See
     also the scope attribute.
scope = scope-name [CI]
     This attribute specifies the set of data cells for which the current
     header cell provides header information. This attribute may be used in
     place of the headers attribute, particularly for simple tables. When
     specified, this attribute must have one of the following values:
        o row: The current cell provides header information for the rest of
          the row that contains it (see also the section on table
          directionality).
        o col: The current cell provides header information for the rest of
          the column that contains it.
        o rowgroup: The header cell provides header information for the rest
          of the row group that contains it.
        o colgroup: The header cell provides header information for the rest
          of the column group that contains it.
abbr = text [CS]
     This attribute should be used to provide an abbreviated form of the
     cell's content, and may be rendered by user agents when appropriate in
     place of the cell's content. Abbreviated names should be short since
     user agents may render them repeatedly. For instance, speech
     synthesizers may render the abbreviated headers relating to a
     particular cell before rendering that cell's content.
axis = cdata [CI]
     This attribute may be used to place a cell into conceptual categories
     that can be considered to form axes in an n-dimensional space. User
     agents may give users access to these categories (e.g., the user may
     query the user agent for all cells that belong to certain categories,
     the user agent may present a table in the form of a table of contents,
     etc.). Please consult the section on categorizing cells for more
     information. The value of this attribute is a comma-separated list of
     category names.
rowspan = number [CN]
     This attribute specifies the number of rows spanned by the current
     cell. The default value of this attribute is one ("1"). The value zero
     ("0") means that the cell spans all rows from the current row to the
     last row of the table.
colspan = number [CN]
     This attribute specifies the number of columns spanned by the current
     cell. The default value of this attribute is one ("1"). The value zero
     ("0") means that the cell spans all columns from the current column to
     the last column of the table.
nowrap [CI]
     Deprecated. When present, this boolean attribute tells visual user
     agents to disable automatic text wrapping for this cell. Style sheets
     should be used instead of this attribute to achieve wrapping effects.
     Note. if used carelessly, this attribute may result in excessively wide
     cells.
width = pixels [CN]
     Deprecated. This attribute supplies user agents with a recommended cell
     width.
height = pixels [CN]
     Deprecated. This attribute supplies user agents with a recommended cell
     height.

Attributes defined elsewhere

   * id, class (document-wide identifiers)
   * lang (language information), dir (text direction)
   * title (element title)
   * style (inline style information )
   * onclick, ondblclick, onmousedown, onmouseup, onmouseover, onmousemove,
     onmouseout, onkeypress, onkeydown, onkeyup (intrinsic events )
   * bgcolor (background color)
   * align, char, charoff, valign (cell alignment)

Table cells may contain two types of information: header information and
data. This distinction enables user agents to render header and data cells
distinctly, even in the absence of style sheets. For example, visual user
agents may present header cell text with a bold font. Speech synthesizers
may render header information with a distinct voice inflection.

The TH element defines a cell that contains header information. User agents
have two pieces of header information available: the contents of the TH
element and the value of the abbr attribute. User agents must render either
the contents of the cell or the value of the abbr attribute. For visual
media, the latter may be appropriate when there is insufficient space to
render the full contents of the cell. For non-visual media abbr may be used
as an abbreviation for table headers when these are rendered along with the
contents of the cells to which they apply.

The headers and scope attributes also allow authors to help non-visual user
agents process header information. Please consult the section on labeling
cells for non-visual user agents for information and examples.

The TD element defines a cell that contains data.

Cells may be empty (i.e., contain no data).

For example, the following table contains four columns of data, each headed
by a column description.

<TABLE summary="This table charts the number of cups
                   of coffee consumed by each senator, the type
                   of coffee (decaf or regular), and whether
                   taken with sugar.">
<CAPTION>Cups of coffee consumed by each senator</CAPTION>
<TR>
   <TH>Name</TH>
   <TH>Cups</TH>
   <TH>Type of Coffee</TH>
   <TH>Sugar?</TH>
<TR>
   <TD>T. Sexton</TD>
   <TD>10</TD>
   <TD>Espresso</TD>
   <TD>No</TD>
<TR>
   <TD>J. Dinnen</TD>
   <TD>5</TD>
   <TD>Decaf</TD>
   <TD>Yes</TD>
</TABLE>

A user agent rendering to a tty device might display this as follows:

Name         Cups       Type of Coffee   Sugar?
T. Sexton    10         Espresso         No
J. Dinnen    5          Decaf            Yes

Cells that span several rows or columns

Cells may span several rows or columns. The number of rows or columns
spanned by a cell is set by the rowspan and colspan attributes for the TH
and TD elements.

In this table definition, we specify that the cell in row four, column two
should span a total of three columns, including the current row.

<TABLE border="1">
<CAPTION>Cups of coffee consumed by each senator</CAPTION>
<TR><TH>Name<TH>Cups<TH>Type of Coffee<TH>Sugar?
<TR><TD>T. Sexton<TD>10<TD>Espresso<TD>No
<TR><TD>J. Dinnen<TD>5<TD>Decaf<TD>Yes
<TR><TD>A. Soria<TD colspan="3"><em>Not available</em>
</TABLE>

This table might be rendered on a tty device by a visual user agent as
follows:

Cups of coffee consumed by each senator
 --------------------------------------
 |   Name  |Cups|Type of Coffee|Sugar?|
 --------------------------------------
 |T. Sexton|10  |Espresso      |No    |
 --------------------------------------
 |J. Dinnen|5   |Decaf         |Yes   |
 --------------------------------------
 |A. Soria |Not available             |
 --------------------------------------

The next example illustrates (with the help of table borders) how cell
definitions that span more than one row or column affect the definition of
later cells. Consider the following table definition:

<TABLE border="1">
<TR><TD>1 <TD rowspan="2">2 <TD>3
<TR><TD>4 <TD>6
<TR><TD>7 <TD>8 <TD>9
</TABLE>

As cell "2" spans the first and second rows, the definition of the second
row will take it into account. Thus, the second TD in row two actually
defines the row's third cell. Visually, the table might be rendered to a tty
device as:

-------------
| 1 | 2 | 3 |
----|   |----
| 4 |   | 6 |
----|---|----
| 7 | 8 | 9 |
-------------

while a graphical user agent might render this as:

[Image of a table with rowspan=2]

Note that if the TD defining cell "6" had been omitted, an extra empty cell
would have been added by the user agent to complete the row.

Similarly, in the following table definition:

<TABLE border="1">
<TR><TD>1 <TD>2 <TD>3
<TR><TD colspan="2">4 <TD>6
<TR><TD>7 <TD>8 <TD>9
</TABLE>

cell "4" spans two columns, so the second TD in the row actually defines the
third cell ("6"):

-------------
| 1 | 2 | 3 |
--------|----
| 4     | 6 |
--------|----
| 7 | 8 | 9 |
-------------

A graphical user agent might render this as:

[Image of a table with colspan=2]

Defining overlapping cells is an error. User agents may vary in how they
handle this error (e.g., rendering may vary).

The following illegal example illustrates how one might create overlapping
cells. In this table, cell "5" spans two rows and cell "7" spans two
columns, so there is overlap in the cell between "7" and "9":

<TABLE border="1">
<TR><TD>1 <TD>2 <TD>3
<TR><TD>4 <TD rowspan="2">5 <TD>6
<TR><TD colspan="2">7 <TD>9
</TABLE>

11.3 Table formatting by visual user agents

Note.The following sections describe the HTML table attributes that concern
visual formatting. Although style sheets will offer better control of visual
table formatting, at the writing of this specification, [CSS1] did not offer
mechanisms to control all aspects of visual table formatting.

HTML 4.0 includes mechanisms to control:

   * border styles
   * horizontal and vertical alignment of cell contents
   * and cell margins

11.3.1 Borders and rules

The following attributes affect a table's external frame and internal rules.

Attribute definitions

frame = void|above|below|hsides|lhs|rhs|vsides|box|border [CI]
     This attribute specifies which sides of the frame that surrounds a
     table will be visible. Possible values:
        o void: No sides. This is the default value.
        o above: The top side only.
        o below: The bottom side only.
        o hsides: The top and bottom sides only.
        o vsides: The right and left sides only.
        o lhs: The left-hand side only.
        o rhs: The right-hand side only.
        o box: All four sides.
        o border: All four sides.
rules = none|groups|rows|cols|all [CI]
     This attribute specifies which rules will appear between cells within a
     table. The rendering of rules is user agent dependent. Possible values:
        o none: No rules. This is the default value.
        o groups: Rules will appear between row groups (see THEAD, TFOOT,
          and TBODY) and column groups (see COLGROUP and COL) only.
        o rows: Rules will appear between rows only.
        o cols: Rules will appear between columns only.
        o all: Rules will appear between all rows and columns.
border = pixels [CN]
     This attributes specifies the width (in pixels only) of the frame
     around a table (see the Note below for more information about this
     attribute).

To help distinguish the cells of a table, we can set the border attribute of
the TABLE element. Consider a previous example:

<TABLE border="1"
       summary="This table charts the number of cups
                of coffee consumed by each senator, the type
                of coffee (decaf or regular), and whether
                taken with sugar.">
<CAPTION>Cups of coffee consumed by each senator</CAPTION>
<TR>
   <TH>Name</TH>
   <TH>Cups</TH>
   <TH>Type of Coffee</TH>
   <TH>Sugar?</TH>
<TR>
   <TD>T. Sexton</TD>
   <TD>10</TD>
   <TD>Espresso</TD>
   <TD>No</TD>
<TR>
   <TD>J. Dinnen</TD>
   <TD>5</TD>
   <TD>Decaf</TD>
   <TD>Yes</TD>
</TABLE>

In the following example, the user agent should show borders five pixels
thick on the left-hand and right-hand sides of the table, with rules drawn
between each column.

<TABLE border="5" frame="vsides" rules="cols">
<TR> <TD>1 <TD>2 <TD>3
<TR> <TD>4 <TD>5 <TD>6
<TR> <TD>7 <TD>8 <TD>9
</TABLE>

The following settings should be observed by user agents for backwards
compatibility.

   * Setting border="0" implies frame="void" and, unless otherwise
     specified, rules="none".
   * Other values of border imply frame="border" and, unless otherwise
     specified, rules="all".
   * The value "border" in the start tag of the TABLE element should be
     interpreted as the value of the frame attribute. It implies rules="all"
     and some default (non-zero) value for the border attribute.

For example, the following definitions are equivalent:

<TABLE border="2">
<TABLE border="2" frame="border" rules="all">

as are the following:

<TABLE border>
<TABLE frame="border" rules="all">

Note. The border attribute also defines the border behavior for the OBJECT
and IMG elements, but takes different values for those elements.

11.3.2 Horizontal and vertical alignment

The following attributes may be set for different table elements (see their
definitions).

<!-- horizontal alignment attributes for cell contents -->
<!ENTITY % cellhalign
  "align      (left|center|right|justify|char) #IMPLIED
   char       %Character;    #IMPLIED  -- alignment char, e.g. char=':' --
   charoff    %Length;       #IMPLIED  -- offset for alignment char --"
  >
<!-- vertical alignment attributes for cell contents -->
<!ENTITY % cellvalign
  "valign     (top|middle|bottom|baseline) #IMPLIED"
  >

Attribute definitions

align = left|center|right|justify|char [CI]
     This attribute specifies the alignment of data and the justification of
     text in a cell. Possible values:
        o left: Left-flush data/Left-justify text. This is the default value
          for table data.
        o center: Center data/Center-justify text. This is the default value
          for table headers.
        o right: Right-flush data/Right-justify text.
        o justify: Double-justify text.
        o char:Align text around a specific character.
valign = top|middle|bottom|baseline [CI]
     This attribute specifies the vertical position of data within a cell.
     Possible values:
        o top: Cell data is flush with the top of the cell.
        o middle: Cell data is centered vertically within the cell. This is
          the default value.
        o bottom: Cell data is flush with the bottom of the cell.
        o baseline: All cells in the same row as a cell whose valign
          attribute has this value should have their textual data positioned
          so that the first text line occurs on a baseline common to all
          cells in the row. This constraint does not apply to subsequent
          text lines in these cells.
char = character [CN]
     This attribute specifies a single character within a text fragment to
     act as an axis for alignment. The default value for this attribute is
     the decimal point character for the current language as set by the lang
     attribute (e.g., the period (".") in English and the comma (",") in
     French). User agents are not required to support this attribute.
charoff = length [CN]
     When present, this attribute specifies the offset to the first
     occurrence of the alignment character on each line. If a line doesn't
     include the alignment character, it should be horizontally shifted to
     end at the alignment position.

     When charoff is used to set the offset of an alignment character, the
     direction of offset is determined by the current text direction (set by
     the dir attribute). In left-to-right texts (the default), offset is
     from the left margin. In right-to-left texts, offset is from the right
     margin. User agents are not required to support this attribute.

The table in this example aligns a row of currency values along a decimal
point. We set the alignment character to "." explicitly.

<TABLE border="1">
<COLGROUP>
<COL><COL align="char" char=".">
<THEAD>
<TR><TH>Vegetable <TH>Cost per kilo
<TBODY>
<TR><TD>Lettuce        <TD>$1
<TR><TD>Silver carrots <TD>$10.50
<TR><TD>Golden turnips <TD>$100.30
</TABLE>

The formatted table may resemble the following:

------------------------------
|   Vegetable  |Cost per kilo|
|--------------|-------------|
|Lettuce       |        $1   |
|--------------|-------------|
|Silver carrots|       $10.50|
|--------------|-------------|
|Golden turnips|      $100.30|
------------------------------

When the contents of a cell contain more than one instance of the alignment
character specified by char and the contents wrap, user agent behavior is
undefined. Authors should therefore be attentive in their use of char.

Note. Visual user agents typically render TH elements vertically and
horizontally centered within the cell and with a bold font weight.

Inheritance of alignment specifications

The alignment of cell contents can be specified on a cell by cell basis, or
inherited from enclosing elements, such as the row, column or the table
itself.

The order of precedence (from highest to lowest) for the attributes align,
char, and charoff is the following:

  1. An alignment attribute set on an element within a cell's data (e.g.,
     P).
  2. An alignment attribute set on a cell (TH and TD).
  3. An alignment attribute set on a column grouping element (COL and
     COLGROUP). When a cell is part of a multi-column span, the alignment
     property is inherited from the cell definition at the beginning of the
     span.
  4. An alignment attribute set on a row or row grouping element (TR, THEAD,
     TFOOT, and TBODY). When a cell is part of a multi-row span, the
     alignment property is inherited from the cell definition at the
     beginning of the span.
  5. An alignment attribute set on the table (TABLE).
  6. The default alignment value.

The order of precedence (from highest to lowest) for the attribute valign
(as well as the other inherited attributes lang, dir, and style) is the
following:

  1. An attribute set on an element within a cell's data (e.g., P).
  2. An attribute set on a cell (TH and TD).
  3. An attribute set on a row or row grouping element (TR, THEAD, TFOOT,
     and TBODY). When a cell is part of a multi-row span, the attribute
     value is inherited from the cell definition at the beginning of the
     span.
  4. An attribute set on a column grouping element (COL and COLGROUP). When
     a cell is part of a multi-column span, the attribute value is inherited
     from the cell definition at the beginning of the span.
  5. An attribute set on the table (TABLE).
  6. The default attribute value.

Furthermore, when rendering cells, horizontal alignment is determined by
columns in preference to rows, while for vertical alignment, rows are given
preference over columns.

The default alignment for cells depends on the user agent. However, user
agents should substitute the default attribute for the current
directionality (i.e., not just "left" in all cases).

User agents that do not support the "justify" value of the align attribute
should use the value of the inherited directionality in its place.

Note. Note that a cell may inherit an attribute not from its parent but from
the first cell in a span. This is an exception to the general attribute
inheritance rules.

11.3.3 Cell margins

Attribute definitions

cellspacing = length [CN]
     This attribute specifies how much space the user agent should leave
     between the left side of the table and the left-hand side of the
     leftmost column, the top of the table and the top side of the topmost
     row, and so on for the right and bottom of the table. The attribute
     also specifies the amount of space to leave between cells.
cellpadding = length [CN]
     This attribute specifies the amount of space between the border of the
     cell and its contents. If the value of this attribute is a pixel
     length, all four margins should be this distance from the contents. If
     the value of the attribute is a percentage length, the top and bottom
     margins should be equally separated from the content based on a
     percentage of the available vertical space, and the left and right
     margins should be equally separated from the content based on a
     percentage of the available horizontal space.

These two attributes control spacing between and within cells. The following
illustration explains how they relate:

  [Image illustrating how cellspacing and cellpadding attributes relate.]

In the following example, the cellspacing attribute specifies that cells
should be separated from each other and from the table frame by twenty
pixels. The cellpadding attribute specifies that the top margin of the cell
and the bottom margin of the cell will each be separated from the cell's
contents by 10% of the available vertical space (the total being 20%).
Similarly, the left margin of the cell and the right margin of the cell will
each be separated from the cell's contents by 10% of the available
horizontal space (the total being 20%).

<TABLE cellspacing="20" cellpadding="20%">
<TR> <TD>Data1 <TD>Data2 <TD>Data3
</TABLE>

If a table or given column has a fixed width, cellspacing and cellpadding
may demand more space than assigned. User agents may give these attributes
precedence over the width attribute when a conflict occurs, but are not
required to.

11.4 Table rendering by non-visual user agents

11.4.1 Associating header information with data cells

Non-visual user agents such as speech synthesizers and Braille-based devices
may use the following TD and TH element attributes to render table cells
more intuitively:

   * For a given data cell, the headers attribute lists which cells provide
     pertinent header information. For this purpose, each header cell must
     be named using the id attribute. Note that its not always possible to
     make a clean division of cells into headers or data. You should use the
     TD element for such cells together with the id or scope attributes as
     appropriate.
   * For a given header cell, the scope attribute tells the user agent the
     data cells for which this header provides information. Authors may
     choose to use this attribute instead of headers according to which is
     more convenient; the two attributes fulfill the same function. The
     headers attribute is generally needed when headers are placed in
     irregular positions with respect to the data they apply to.
   * The abbr attribute specifies an abbreviated header for header cells so
     that user agents may render header information more rapidly.

In the following example, we assign header information to cells by setting
the headers attribute. Each cell in the same column refers to the same
header cell (via the id attribute).

<TABLE border="1"
       summary="This table charts the number of cups
                of coffee consumed by each senator, the type
                of coffee (decaf or regular), and whether
                taken with sugar.">
<CAPTION>Cups of coffee consumed by each senator</CAPTION>
<TR>
   <TH id="t1">Name</TH>
   <TH id="t2">Cups</TH>
   <TH id="t3" abbr="Type">Type of Coffee</TH>
   <TH id="t4">Sugar?</TH>
<TR>
   <TD headers="t1">T. Sexton</TD>
   <TD headers="t2">10</TD>
   <TD headers="t3">Espresso</TD>
   <TD headers="t4">No</TD>
<TR>
   <TD headers="t1">J. Dinnen</TD>
   <TD headers="t2">5</TD>
   <TD headers="t3">Decaf</TD>
   <TD headers="t4">Yes</TD>
</TABLE>

A speech synthesizer might render this table as follows:

Caption: Cups of coffee consumed by each senator
Summary: This table charts the number of cups
         of coffee consumed by each senator, the type
         of coffee (decaf or regular), and whether
         taken with sugar.
Name: T. Sexton,   Cups: 10,   Type: Espresso,   Sugar: No
Name: J. Dinnen,   Cups: 5,    Type: Decaf,      Sugar: Yes

Note how the header "Type of Coffee" is abbreviated to "Type" using the abbr
attribute.

Here is the same example substituting the scope attribute for the headers
attribute. Note the value "col" for the scope attribute, meaning "all cells
in the current column":

<TABLE border="1"
       summary="This table charts the number of cups
                of coffee consumed by each senator, the type
                of coffee (decaf or regular), and whether
                taken with sugar.">
<CAPTION>Cups of coffee consumed by each senator</CAPTION>
<TR>
   <TH scope="col">Name</TH>
   <TH scope="col">Cups</TH>
   <TH scope="col" abbr="Type">Type of Coffee</TH>
   <TH scope="col">Sugar?</TH>
<TR>
   <TD>T. Sexton</TD>
   <TD>10</TD>
   <TD>Espresso</TD>
   <TD>No</TD>
<TR>
   <TD>J. Dinnen</TD>
   <TD>5</TD>
   <TD>Decaf</TD>
   <TD>Yes</TD>
</TABLE>

Here's a somewhat more complex example illustrating other values for the
scope attribute:

<TABLE border="1" cellpadding="5" cellspacing="2"
  summary="History courses offered in the community of
           Bath arranged by course name, tutor, summary,
           code, and fee">
  <TR>
    <TH colspan="5" scope="colgroup">Community Courses -- Bath Autumn 1997</TH>
  </TR>
  <TR>
    <TH scope="col" abbr="Name">Course Name</TH>
    <TH scope="col" abbr="Tutor">Course Tutor</TH>
    <TH scope="col">Summary</TH>
    <TH scope="col">Code</TH>
    <TH scope="col">Fee</TH>
  </TR>
  <TR>
    <TD scope="row">After the Civil War</TD>
    <TD>Dr. John Wroughton</TD>
    <TD>
       The course will examine the turbulent years in England
       after 1646. <EM>6 weekly meetings starting Monday 13th
      October.</EM>
    </TD>
    <TD>H27</TD>
    <TD>&pound;32</TD>
  </TR>
  <TR>
    <TD scope="row">An Introduction to Anglo-Saxon England</TD>
    <TD>Mark Cottle</TD>
    <TD>
       One day course introducing the early medieval
       period reconstruction the Anglo-Saxons and
       their society. <EM>Saturday 18th October.</EM>
    </TD>
    <TD>H28</TD>
    <TD>&pound;18</TD>
  </TR>
  <TR>
    <TD scope="row">The Glory that was Greece</TD>
    <TD>Valerie Lorenz</TD>
    <TD>
     Birthplace of democracy, philosophy, heartland of theater, home of
     argument. The Romans may have done it but the Greeks did it
     first. <EM>Saturday day school 25th October 1997</EM>
    </TD>
    <TD>H30</TD>
    <TD>&pound;18</TD>
  </TR>
</TABLE>

A graphical user agent might render this as:

[A table with merged cells]

Note the use of the scope attribute with the "row" value. Although the first
cell in each row contains data, not header information, the scope attribute
makes the data cell behave like a row header cell. This allows speech
synthesizers to provide the relevant course name upon request or to state it
immediately before each cell's content.

11.4.2 Categorizing cells

Users browsing a table with a speech-based user agent may wish to hear an
explanation of a cell's contents in addition to the contents themselves. One
way the user might provide an explanation is by speaking associated header
information before speaking the data cell's contents (see the section on
associating header information with data cells).

Users may also want information about more than one cell, in which case
header information provided at the cell level (by headers, scope, and abbr)
may not provide adequate context. Consider the following table, which
classifies expenses for meals, hotels, and transport in two locations (San
Jose and Seattle) over several days:

[Image of a table listing travel expenses at two locations: San Jose and Seattle, by date, and category (meals, hotels, and transport), shown with subtitles]

Users might want to extract information from the table in the form of
queries:

   * "What did I spend for all my meals?"
   * "What did I spend for meals on 25 August?"
   * "What did I spend for all expenses in San Jose?"

Each query involves a computation by the user agent that may involve zero or
more cells. In order to determine, for example, the costs of meals on 25
August, the user agent must know which table cells refer to "Meals" (all of
them) and which refer to "Dates" (specifically, 25 August), and find the
intersection of the two sets.

To accommodate this type of query, the HTML 4.0 table model allows authors
to place cell headers and data into categories. For example, for the travel
expense table, an author could group the header cells "San Jose" and
"Seattle" into the category "Location", the headers "Meals", "Hotels", and
"Transport" in the category "Expenses", and the four days into the category
"Date". The previous three questions would then have the following meanings:

   * "What did I spend for all my meals?" means "What are all the data cells
     in the "Expenses=Meals" category?
   * "What did I spend for meals on 25 August?" means "What are all the data
     cells in the "Expenses=Meals" and "Date=Aug-25-1997" categories?
   * "What did I spend for all expenses in San Jose?" means "What are all
     the data cells in the "Expenses=Meals, Hotels, Transport" and
     "Location=San Jose" categories?

Authors categorize a header or data cell by setting the axis attribute for
the cell. For instance, in the travel expense table, the cell containing the
information "San Jose" could be placed in the "Location" category as
follows:

  <TH id="a6" axis="location">San Jose</TH>

Any cell containing information related to "San Jose" should refer to this
header cell via either the headers or the scope attribute. Thus, meal
expenses for 25-Aug-1997 should be marked up to refer to id attribute (whose
value here is "a6") of the "San Jose" header cell:


  <TD headers="a6">37.74</TD>

Each headers attribute provides a list of id references. Authors may thus
categorize a given cell in any number of ways (or, along any number of
"headers", hence the name).

Below we mark up the travel expense table with category information:

<TABLE border="1"
          summary="This table summarizes travel expenses
                   incurred during August trips to
                   San Jose and Seattle">
<CAPTION>
  Travel Expense Report
</CAPTION>
<TR>
  <TH></TH>
  <TH id="a2" axis="expenses">Meals</TH>
  <TH id="a3" axis="expenses">Hotels</TH>
  <TH id="a4" axis="expenses">Transport</TH>
  <TD>subtotals</TD>
</TR>
<TR>
  <TH id="a6" axis="location">San Jose</TH>
  <TH></TH>
  <TH></TH>
  <TH></TH>
  <TD></TD>
</TR>
<TR>
  <TD id="a7" axis="date">25-Aug-97</TD>
  <TD headers="a6 a7 a2">37.74</TD>
  <TD headers="a6 a7 a3">112.00</TD>
  <TD headers="a6 a7 a4">45.00</TD>
  <TD></TD>
</TR>
<TR>
  <TD id="a8" axis="date">26-Aug-97</TD>
  <TD headers="a6 a8 a2">27.28</TD>
  <TD headers="a6 a8 a3">112.00</TD>
  <TD headers="a6 a8 a4">45.00</TD>
  <TD></TD>
</TR>
<TR>
  <TD>subtotals</TD>
  <TD>65.02</TD>
  <TD>224.00</TD>
  <TD>90.00</TD>
  <TD>379.02</TD>
</TR>
<TR>
  <TH id="a10" axis="location">Seattle</TH>
  <TH></TH>
  <TH></TH>
  <TH></TH>
  <TD></TD>
</TR>
<TR>
  <TD id="a11" axis="date">27-Aug-97</TD>
  <TD headers="a10 a11 a2">96.25</TD>
  <TD headers="a10 a11 a3">109.00</TD>
  <TD headers="a10 a11 a4">36.00</TD>
  <TD></TD>
</TR>
<TR>
  <TD id="a12" axis="date">28-Aug-97</TD>
  <TD headers="a10 a12 a2">35.00</TD>
  <TD headers="a10 a12 a3">109.00</TD>
  <TD headers="a10 a12 a4">36.00</TD>
  <TD></TD>
</TR>
<TR>
  <TD>subtotals</TD>
  <TD>131.25</TD>
  <TD>218.00</TD>
  <TD>72.00</TD>
  <TD>421.25</TD>
</TR>
<TR>
  <TH>Totals</TH>
  <TD>196.27</TD>
  <TD>442.00</TD>
  <TD>162.00</TD>
  <TD>800.27</TD>
</TR>
</TABLE>

Note that marking up the table this way also allows user agents to avoid
confusing the user with unwanted information. For instance, if a speech
synthesizer were to speak all of the figures in the "Meals" column of this
table in response to the query "What were all my meal expenses?", a user
would not be able to distinguish a day's expenses from subtotals or totals.
By carefully categorizing cell data, authors allow user agents to make
important semantic distinctions when rendering.

Of course, there is no limit to how authors may categorize information in a
table. In the travel expense table, for example, we could add the additional
categories "subtotals" and "totals".

This specification does not require user agents to handle information
provided by the axis attribute, nor does it make any recommendations about
how user agents may present axis information to users or how users may query
the user agent about this information.

However, user agents, particularly speech synthesizers, may want to factor
out information common to several cells that are the result of a query. For
instance, if the user asks "What did I spend for meals in San Jose?", the
user agent would first determine the cells in question (25-Aug-1997: 37.74,
26-Aug-1997:27.28), then render this information. A user agent speaking this
information might read it:

   Location: San Jose. Date: 25-Aug-1997. Expenses, Meals: 37.74
   Location: San Jose. Date: 26-Aug-1997. Expenses, Meals: 27.28

or, more compactly:

   San Jose, 25-Aug-1997, Meals: 37.74
   San Jose, 26-Aug-1997, Meals: 27.28

An even more economical rendering would factor the common information and
reorder it:

   San Jose, Meals, 25-Aug-1997: 37.74
                    26-Aug-1997: 27.28

User agents that support this type of rendering should allow user agents a
means to customize rendering (e.g., through style sheets).

11.4.3 Algorithm to find heading information

In the absence of header information from either the scope or headers
attribute, user agents may construct header information according to the
following algorithm. The goal of the algorithm is to find an ordered list of
headers. (In the following description of the algorithm the table
directionality is assumed to be left-to-right.)

   * First, search left from the cell's position to find row header cells.
     Then search upwards to find column header cells. The search in a given
     direction stops when the edge of the table is reached or when a data
     cell is found after a header cell.
   * Row headers are inserted into the list in the order they appear in the
     table. For left-to-right tables, headers are inserted from left to
     right.
   * Column headers are inserted after row headers, in the order they appear
     in the table, from top to bottom.
   * If a header cell has the headers attribute set, then the headers
     referenced by this attribute are inserted into the list and the search
     stops for the current direction.
   * TD cells that set the axis attribute are also treated as header cells.

11.5 Sample table

This sample illustrates grouped rows and columns. The example is adapted
from "Developing International Software", by Nadine Kano.

In "ascii art", the following table:

<TABLE border="2" frame="hsides" rules="groups"
          summary="Code page support in different versions
                   of MS Windows.">
<CAPTION>CODE-PAGE SUPPORT IN MICROSOFT WINDOWS</CAPTION>
<COLGROUP align="center">
<COLGROUP align="left">
<COLGROUP align="center" span="2">
<COLGROUP align="center" span="3">
<THEAD valign="top">
<TR>
<TH>Code-Page<BR>ID
<TH>Name
<TH>ACP
<TH>OEMCP
<TH>Windows<BR>NT 3.1
<TH>Windows<BR>NT 3.51
<TH>Windows<BR>95
<TBODY>
<TR><TD>1200<TD>Unicode (BMP of ISO/IEC-10646)<TD><TD><TD>X<TD>X<TD>*
<TR><TD>1250<TD>Windows 3.1 Eastern European<TD>X<TD><TD>X<TD>X<TD>X
<TR><TD>1251<TD>Windows 3.1 Cyrillic<TD>X<TD><TD>X<TD>X<TD>X
<TR><TD>1252<TD>Windows 3.1 US (ANSI)<TD>X<TD><TD>X<TD>X<TD>X
<TR><TD>1253<TD>Windows 3.1 Greek<TD>X<TD><TD>X<TD>X<TD>X
<TR><TD>1254<TD>Windows 3.1 Turkish<TD>X<TD><TD>X<TD>X<TD>X
<TR><TD>1255<TD>Hebrew<TD>X<TD><TD><TD><TD>X
<TR><TD>1256<TD>Arabic<TD>X<TD><TD><TD><TD>X
<TR><TD>1257<TD>Baltic<TD>X<TD><TD><TD><TD>X
<TR><TD>1361<TD>Korean (Johab)<TD>X<TD><TD><TD>**<TD>X
<TBODY>
<TR><TD>437<TD>MS-DOS United States<TD><TD>X<TD>X<TD>X<TD>X
<TR><TD>708<TD>Arabic (ASMO 708)<TD><TD>X<TD><TD><TD>X
<TR><TD>709<TD>Arabic (ASMO 449+, BCON V4)<TD><TD>X<TD><TD><TD>X
<TR><TD>710<TD>Arabic (Transparent Arabic)<TD><TD>X<TD><TD><TD>X
<TR><TD>720<TD>Arabic (Transparent ASMO)<TD><TD>X<TD><TD><TD>X
</TABLE>

would be rendered something like this:

                  CODE-PAGE SUPPORT IN MICROSOFT WINDOWS
===============================================================================
Code-Page | Name                         | ACP  OEMCP | Windows Windows Windows
    ID    |                              |            |  NT 3.1 NT 3.51    95
-------------------------------------------------------------------------------
   1200   | Unicode (BMP of ISO 10646)   |            |    X       X       *
   1250   | Windows 3.1 Eastern European |  X         |    X       X       X
   1251   | Windows 3.1 Cyrillic         |  X         |    X       X       X
   1252   | Windows 3.1 US (ANSI)        |  X         |    X       X       X
   1253   | Windows 3.1 Greek            |  X         |    X       X       X
   1254   | Windows 3.1 Turkish          |  X         |    X       X       X
   1255   | Hebrew                       |  X         |                    X
   1256   | Arabic                       |  X         |                    X
   1257   | Baltic                       |  X         |                    X
   1361   | Korean (Johab)               |  X         |            **      X
-------------------------------------------------------------------------------
    437   | MS-DOS United States         |        X   |    X       X       X
    708   | Arabic (ASMO 708)            |        X   |                    X
    709   | Arabic (ASMO 449+, BCON V4)  |        X   |                    X
    710   | Arabic (Transparent Arabic)  |        X   |                    X
    720   | Arabic (Transparent ASMO)    |        X   |                    X
===============================================================================

A graphical user agent might render this as:

[A table with grouped rows and columns]

This example illustrates how COLGROUP can be used to group columns and set
the default column alignment. Similarly, TBODY is used to group rows. The
frame and rules attributes tell the user agent which borders and rules to
render.

                                  12 Links

Contents

  1. Introduction to links and anchors
       1. Visiting a linked resource
       2. Other link relationships
       3. Specifying anchors and links
       4. Link titles
       5. Internationalization and links
  2. The A element
       1. Syntax of anchor names
       2. Nested links are illegal
       3. Anchors with the id attribute
       4. Unavailable and unidentifiable resources
  3. Document relationships: the LINK element
       1. Forward and reverse links
       2. Links and external style sheets
       3. Links and search engines
  4. Path information: the BASE element
       1. Resolving relative URIs

12.1 Introduction to links and anchors

HTML offers many of the conventional publishing idioms for rich text and
structured documents, but what separates it from most other markup languages
is its features for hypertext and interactive documents. This section
introduces the link (or hyperlink, or Web link), the basic hypertext
construct. A link is a connection from one Web resource to another. Although
a simple concept, the link has been one of the primary forces driving the
success of the Web.

A link has two ends -- called anchors -- and a direction. The link starts at
the "source" anchor and points to the "destination" anchor, which may be any
Web resource (e.g., an image, a video clip, a sound bite, a program, an HTML
document, an element within an HTML document, etc.).

12.1.1 Visiting a linked resource

The default behavior associated with a link is the retrieval of another Web
resource. This behavior is commonly and implicitly obtained by selecting the
link (e.g., by clicking, through keyboard input, etc.).

The following HTML excerpt contains two links, one whose destination anchor
is an HTML document named "chapter2.html" and the other whose destination
anchor is a GIF image in the file "forest.gif":

<BODY>
...some text...
<P>You'll find a lot more in  <A href="chapter2.html">chapter two</A>.
See also this <A href="../images/forest.gif">map of the enchanted forest.</A>
</BODY>

By activating these links (by clicking with the mouse, through keyboard
input, voice commands, etc.), users may visit these resources. Note that the
hrefattribute in each source anchor specifies the address of the destination
anchor with a URI.

The destination anchor of a link may be an element within an HTML document.
The destination anchor must be given an anchor name and any URI addressing
this anchor must include the name as its fragment identifier.

Destination anchors in HTML documents may be specified either by the A
element (naming it with the name attribute), or by any other element (naming
with the id attribute).

Thus, for example, an author might create a table of contents whose entries
link to header elements H2, H3, etc., in the same document. Using the A
element to create destination anchors, we would write:

<H1>Table of Contents</H1>
<P><A href="#section1">Introduction</A><BR>
<A href="#section2">Some background</A><BR>
<A href="#section2.1">On a more personal note</A><BR>
...the rest of the table of contents...
...the document body...
<H2><A name="section1">Introduction</A></H2>
...section 1...
<H2><A name="section2">Some background</A></H2>
...section 2...
<H3><A name="section2.1">On a more personal note</A></H3>
...section 2.1...

We may achieve the same effect by making the header elements themselves the
anchors:

<H1>Table of Contents</H1>
<P><A href="#section1">Introduction</A><BR>
<A href="#section2">Some background</A><BR>
<A href="#section2.1">On a more personal note</A><BR>
...the rest of the table of contents...
...the document body...
<H2 id="section1">Introduction</H2>
...section 1...
<H2 id="section2">Some background</H2>
...section 2...
<H3 id="section2.1">On a more personal note</H3>
...section 2.1...

12.1.2 Other link relationships

By far the most common use of a link is to retrieve another Web resource, as
illustrated in the previous examples. However, authors may insert links in
their documents that express other relationships between resources than
simply "activate this link to visit that related resource". Links that
express other types of relationships have one or more link type specified in
their source anchor.

The roles of a link defined by A or LINK are specified via the rel and rev
attributes.

For instance, links defined by the LINK element may describe the position of
a document within a series of documents. In the following excerpt, links
within the document entitled "Chapter 5" point to the previous and next
chapters:

<HEAD>
...other head information...
<TITLE>Chapter 5</TITLE>
<LINK rel="prev" href="chapter4.html">
<LINK rel="next" href="chapter6.html">
</HEAD>

The link type of the first link is "prev" and that of the second is "next"
(two of several recognized link types). Links specified by LINK are not
rendered with the document's contents, although user agents may render them
in other ways (e.g., as navigation tools).

Even if they are not used for navigation, these links may be interpreted in
interesting ways. For example, a user agent that prints a series of HTML
documents as a single document may use this link information as the basis of
forming a coherent linear document. Further information is given below of
using links for the benefit of search engines

12.1.3 Specifying anchors and links

Although several HTML elements and attributes create links to other
resources (e.g., the IMG element, the FORM element, etc.), this chapter
discusses links and anchors created by the LINK and A elements. The LINK
element may only appear in the head of a document. The A element may only
appear in the body.

When the A element's href attribute is set, the element defines a source
anchor for a link that may be activated by the user to retrieve a Web
resource. The source anchor is the location of the A instance and the
destination anchor is the Web resource.

The retrieved resource may be handled by the user agent in several ways: by
opening a new HTML document in the same user agent window, opening a new
HTML document in a different window, starting a new program to handle the
resource, etc. Since the A element has content (text, images, etc.), user
agents may render this content in such a way as to indicate the presence of
a link (e.g., by underlining the content).

When the name or id attributes of the A element are set, the element defines
an anchor that may be the destination of other links.

Authors may set the name and href attributes simultaneously in the same A
instance.

The LINK element defines a relationship between the current document and
another resource. Although LINK has no content, the relationships it defines
may be rendered by some user agents.

12.1.4 Link titles

The title attribute may be set for both A and LINK to add information about
the nature of a link. This information may be spoken by a user agent,
rendered as a tool tip, cause a change in cursor image, etc.

Thus, we may augment a previous example by supplying a title for each link:

<BODY>
...some text...
<P>You'll find a lot more in <A href="chapter2.html"
       title="Go to chapter two">chapter two</A>.
<A href="./chapter2.html"
       title="Get chapter two.">chapter two</A>.
See also this <A href="../images/forest.gif"
       title="GIF image of enchanted forest">map of
the enchanted forest.</A>
</BODY>

12.1.5 Internationalization and links

Since links may point to documents encoded with different character
encodings, the A and LINK elements support the charset attribute. This
attribute allows authors to advise user agents about the encoding of data at
the other end of the link.

The hreflang attribute provides user agents about the language of a resource
at the end of a link, just as the lang attribute provides information about
the language of an element's content or attribute values.

Armed with this additional knowledge, user agents should be able to avoid
presenting "garbage" to the user. Instead, they may either locate resources
necessary for the correct presentation of the document or, if they cannot
locate the resources, they should at least warn the user that the document
will be unreadable and explain the cause.

12.2 The A element

<!ELEMENT A - - (%inline;)* -(A)       -- anchor -->
<!ATTLIST A
  %attrs;                              -- %coreattrs, %i18n, %events --
  charset     %Charset;      #IMPLIED  -- char encoding of linked resource --
  type        %ContentType;  #IMPLIED  -- advisory content type --
  name        CDATA          #IMPLIED  -- named link end --
  href        %URI;          #IMPLIED  -- URI for linked resource --
  hreflang    %LanguageCode; #IMPLIED  -- language code --
  rel         %LinkTypes;    #IMPLIED  -- forward link types --
  rev         %LinkTypes;    #IMPLIED  -- reverse link types --
  accesskey   %Character;    #IMPLIED  -- accessibility key character --
  shape       %Shape;        rect      -- for use with client-side image maps --
  coords      %Coords;       #IMPLIED  -- for use with client-side image maps --
  tabindex    NUMBER         #IMPLIED  -- position in tabbing order --
  onfocus     %Script;       #IMPLIED  -- the element got the focus --
  onblur      %Script;       #IMPLIED  -- the element lost the focus --
  >

Start tag: required, End tag: required

Attribute definitions

name = cdata [CS]
     This attribute names the current anchor so that it may be the
     destination of another link. The value of this attribute must be a
     unique anchor name. The scope of this name is the current document.
     Note that this attribute shares the same name space as the id
     attribute.
href = uri [CT]
     This attribute specifies the location of a Web resource, thus defining
     a link between the current element (the source anchor) and the
     destination anchor defined by this attribute.
hreflang = langcode [CI]
     This attribute specifies the base language of the resource designated
     by href and may only be used when href is specified.
type = content-type [CI]
     When present, this attribute specifies the content type of a piece of
     content, for example, the result of dereferencing a resource. Content
     types are defined in [MIMETYPES].
rel = link-types [CI]
     This attribute describes the relationship from the current document to
     the anchor specified by the href attribute. The value of this attribute
     is a space-separated list of link types.
rev = link-types [CI]
     This attribute is used to describe a reverse link from the anchor
     specified by the href attribute to the current document. The value of
     this attribute is a space-separated list of link types.
charset = charset [CI]
     This attribute specifies the character encoding of the resource
     designated by the link. Please consult the section on character
     encodings for more details.

Attributes defined elsewhere

   * id, class (document-wide identifiers)
   * lang (language information), dir (text direction)
   * title (element title)
   * style (inline style information )
   * shape and coords (image maps)
   * onfocus, onblur, onclick, ondblclick, onmousedown, onmouseup,
     onmouseover, onmousemove, onmouseout, onkeypress, onkeydown, onkeyup
     (intrinsic events )
   * target (target frame information)
   * tabindex (tabbing navigation)
   * accesskey (access keys)

Each A element defines an anchor

  1. The A element's content defines the position of the anchor.
  2. The name attribute names the anchor so that it may be the destination
     of zero or more links (see also anchors with id).
  3. The href attribute makes this anchor the source anchor of exactly one
     link.

Authors may also create an A element that specifies no anchors, i.e., that
doesn't specify href, name, or id. Values for these attributes may be set at
a later time through scripts.

In the example that follows, the A element defines a link. The source anchor
is the text "W3C Web site" and the destination anchor is
"http://www.w3.org/":

For more information about W3C, please consult the
<A href="http://www.w3.org/">W3C Web site</A>.

This link designates the home page of the World Wide Web Consortium. When a
user activates this link in a user agent, the user agent will retrieve the
resource, in this case, an HTML document.

User agents generally render links in such a way as to make them obvious to
users (underlining, reverse video, etc.). The exact rendering depends on the
user agent. Rendering may vary according to whether the user has already
visited the link or not. A possible visual rendering of the previous link
might be:

For more information about W3C, please consult the W3C Web site.
                                                   ~~~~~~~~~~~~

To tell user agents explicitly what the character encoding of the
destination page is, set the charset attribute:

For more information about W3C, please consult the
<A href="http://www.w3.org/" charset="ISO-8859-1">W3C Web site</A>

Suppose we define an anchor named "anchor-one" in the file "one.html".

...text before the anchor...
<A name="anchor-one">This is the location of anchor one.</A>
...text after the anchor...

This creates an anchor around the text "This is the location of anchor
one.". Usually, the contents of A are not rendered in any special way when A
defines an anchor only.

Having defined the anchor, we may link to it from the same or another
document. URIs that designate anchors contain a "#" character followed by
the anchor name (the fragment identifier). Here are some examples of such
URIs:

   * An absolute URI: http://www.mycompany.com/one.html#anchor-one
   * A relative URI: ./one.html#anchor-one or one.html#anchor-one
   * When the link is defined in the same document: #anchor-one

Thus, a link defined in the file "two.html" in the same directory as
"one.html" would refer to the anchor as follows:

...text before the link...
For more information, please consult <A href="./one.html#anchor-one"> anchor one</A>.
...text after the link...

The A element in the following example specifies a link (with href) and
creates a named anchor (with name) simultaneously:

I just returned from vacation! Here's a
<A name="anchor-two"
   href="http://www.somecompany.com/People/Ian/vacation/family.png">
photo of my family at the lake.</A>.

This example contains a link to a different type of Web resource (a PNG
image). Activating the link should cause the image resource to be retrieved
from the Web (and possibly displayed if the system has been configured to do
so).

Note. User agents should be able to find anchors created by empty A
elements, but some fail to do so. For example, some user agents may not find
the "empty-anchor" in the following HTML fragment:

<A name="empty-anchor"></A>
<EM>...some HTML...</EM>
<A href="#empty-anchor">Link to empty anchor</A>

12.2.1 Syntax of anchor names

An anchor name is the value of either the name or id attribute when used in
the context of anchors. Anchor names must observe the following rules:

   * Uniqueness: Anchor names must be unique within a document. Anchor names
     that differ only in case may not appear in the same document.
   * String matching: Comparisons between fragment identifiers and anchor
     names must be done by exact (case-sensitive) match.

Thus, the following example is correct with respect to string matching and
must be considered a match by user agents:

<P><A href="#xxx">...</A>
...more document...
<P><A name="xxx">...</A>

ILLEGAL EXAMPLE:
The following example is illegal with respect to uniqueness since the two
names are the same except for case:

<P><A name="xxx">...</A>
<P><A name="XXX">...</A>

Although the following excerpt is legal HTML, the behavior of the user agent
is not defined; some user agents may (incorrectly) consider this a match and
others may not.

<P><A href="#xxx">...</A>
...more document...
<P><A name="XXX">...</A>

Anchor names should be restricted to ASCII characters. Please consult the
appendix for more information about non-ASCII characters in URI attribute
values.

12.2.2 Nested links are illegal

Links and anchors defined by the A element must not be nested; an A element
must not contain any other A elements.

Since the DTD defines LINK element to be empty, LINK elements may not be
nested either.

12.2.3 Anchors with the id attribute

The id attribute may be used to create an anchor at the start tag of any
element (including the A element).

This example illustrates the use of the id attribute to position an anchor
in an H2 element. The anchor is linked to via the A element.

You may read more about this in <A href="#section2">Section Two</A>.
...later in the document
<H2 id="section2">Section Two</H2>
...later in the document
<P>Please refer to <A href="#section2">Section Two</A> above
for more details.

The following example names a destination anchor with the id attribute:

I just returned from vacation! Here's a
<A id="anchor-two">photo of my family at the lake.</A>.

The id and name attributes share the same name space. This means that they
cannot both define an anchor with the same name in the same document.

ILLEGAL EXAMPLE:
The following excerpt is illegal HTML since these attributes declare the
same name twice in the same document.

<A href="#a1">...</A>
...
<H1 id="a1">
...pages and pages...
<A name="a1"></A>

Because of its specification in the HTML DTD, the name attribute may contain
character references. Thus, the value D&#xfc;rst is a valid name attribute
value, as is D&uuml;rst . The id attribute, on the other hand, may not
contain character references.

Use id or name? Authors should consider the following issues when deciding
whether to use id or name for an anchor name:

   * The id attribute can act as more than just an anchor name (e.g., style
     sheet selector, processing identifier, etc.).
   * Some older user agents don't support anchors created with the id
     attribute.
   * The name attribute allows richer anchors names (with entities).

12.2.4 Unavailable and unidentifiable resources

A reference to an unavailable or unidentifiable resource is an error.
Although user agents may vary in how they handle such an error, we recommend
the following behavior:

   * If a user agent cannot locate a linked resource, it should alert the
     user.
   * If a user agent cannot identify the type of a linked resource, it
     should still attempt to process it. It should alert the user and may
     allow the user to intervene and identify the document type.

12.3 Document relationships: the LINK element

<!ELEMENT LINK - O EMPTY               -- a media-independent link -->
<!ATTLIST LINK
  %attrs;                              -- %coreattrs, %i18n, %events --
  charset     %Charset;      #IMPLIED  -- char encoding of linked resource --
  href        %URI;          #IMPLIED  -- URI for linked resource --
  hreflang    %LanguageCode; #IMPLIED  -- language code --
  type        %ContentType;  #IMPLIED  -- advisory content type --
  rel         %LinkTypes;    #IMPLIED  -- forward link types --
  rev         %LinkTypes;    #IMPLIED  -- reverse link types --
  media       %MediaDesc;    #IMPLIED  -- for rendering on these media --
  >

Start tag: required, End tag: forbidden

Attributes defined elsewhere

   * id, class (document-wide identifiers)
   * lang (language information), dir (text direction)
   * title (element title)
   * style (inline style information )
   * onclick, ondblclick, onmousedown, onmouseup, onmouseover, onmousemove,
     onmouseout, onkeypress, onkeydown, onkeyup (intrinsic events )
   * href, hreflang, type, rel, rev (links and anchors)
   * target (target frame information)
   * media (header style information)
   * charset(character encodings)

This element defines a link. Unlike A, it may only appear in the HEAD
section of a document, although it may appear any number of times. Although
LINK has no content, it conveys relationship information that may be
rendered by user agents in a variety of ways (e.g., a tool-bar with a
drop-down menu of links).

This example illustrates how several LINK definitions may appear in the HEAD
section of a document. The current document is "Chapter2.html". The rel
attribute specifies the relationship of the linked document with the current
document. The values "Index", "Next", and "Prev" are explained in the
section on link types.

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0//EN"
   "http://www.w3.org/TR/REC-html40/strict.dtd">
<HTML>
<HEAD>
  <TITLE>Chapter 2</TITLE>
  <LINK rel="Index" href="../index.html">
  <LINK rel="Next"  href="Chapter3.html">
  <LINK rel="Prev"  href="Chapter1.html">
</HEAD>
...the rest of the document...

12.3.1 Forward and reverse links

The rel and rev attributes play complementary roles -- the rel attribute
specifies a forward link and the rev attribute specifies a reverse link.

Consider two documents A and B.

Document A:       <LINK href="docB" rel="foo">

Has exactly the same meaning as:

Document B:       <LINK href="docA" rev="foo">

Both attributes may be specified simultaneously.

12.3.2 Links and external style sheets

When the LINK element links an external style sheet to a document, the type
attribute specifies the style sheet language and the media attribute
specifies the intended rendering medium or media. User agents may save time
by retrieving from the network only those style sheets that apply to the
current device.

Media types are further discussed in the section on style sheets.

12.3.3 Links and search engines

Authors may use the LINK element to provide a variety of information to
search engines, including:

   * Links to alternate versions of a document, written in another human
     language.
   * Links to alternate versions of a document, designed for different
     media, for instance a version especially suited for printing.
   * Links to the starting page of a collection of documents.

The examples below illustrate how language information, media types, and
link types may be combined to improve document handling by search engines.

In the following example, we use the hreflang attribute to tell search
engines where to find Dutch, Portuguese, and Arabic versions of a document.
Note the use of the dir and charset attributes for the Arabic manual, and
the use of the lang attribute to indicate that the value of the title
attribute for the LINK element designating the French manual is in French.

<HEAD>
<TITLE>The manual in English</TITLE>
<LINK title="The manual in Dutch"
      type="text/html"
      rel="alternate"
      hreflang="nl"
      href="http://someplace.com/manual/dutch.html">
<LINK title="The manual in Portuguese"
      type="text/html"
      rel="alternate"
      hreflang="pt"
      href="http://someplace.com/manual/portuguese.html">
<LINK title="The manual in Arabic"
      dir="rtl"
      type="text/html"
      rel="alternate"
      charset="ISO-8859-6"
      hreflang="ar"
      href="http://someplace.com/manual/arabic.html">
<LINK lang="fr" title="La documentation en Fran&ccedil;ais"
      type="text/html"
      rel="alternate"
      hreflang="fr"
      href="http://someplace.com/manual/french.html">
</HEAD>

In the following example, we tell search engines where to find the printed
version of a manual.

<HEAD>
<TITLE>Reference manual</TITLE>
<LINK media="print" title="The manual in postscript"
      type="application/postscript"
      rel="alternate"
      href="http://someplace.com/manual/postscript.ps">
</HEAD>

In the following example, we tell search engines where to find the front
page of a collection of documents.

<HEAD>
<TITLE>Reference manual -- Page 5</TITLE>
<LINK rel="Start" title="The first page of the manual"
      type="text/html"
      href="http://someplace.com/manual/start.html">
</HEAD>

Further information is given in the notes in the appendix on helping search
engines index your Web site.

12.4 Path information: the BASE element

<!ELEMENT BASE - O EMPTY               -- document base URI -->
<!ATTLIST BASE
  href        %URI;          #REQUIRED -- URI that acts as base URI --
  >

Start tag: required, End tag: forbidden

Attribute definitions

href = uri [CT]
     This attribute specifies an absolute URI that acts as the base URI for
     resolving relative URIs.

Attributes defined elsewhere

   * target (target frame information)

In HTML, links and references to external images, applets, form-processing
programs, style sheets, etc. are always specified by a URI. Relative URIs
are resolved according to a base URI, which may come from a variety of
sources. The BASE element allows authors to specify a document's base URI
explicitly.

When present, the BASE element must appear in the HEAD section of an HTML
document, before any element that refers to an external source. The path
information specified by the BASE element only affects URIs in the document
where the element appears.

For example, given the following BASE declaration and A declaration:

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0//EN"
   "http://www.w3.org/TR/REC-html40/strict.dtd">
<HTML>
 <HEAD>
   <TITLE>Our Products</TITLE>
   <BASE href="http://www.aviary.com/products/intro.html">
 </HEAD>

 <BODY>
   <P>Have you seen our <A href="../cages/birds.gif">Bird Cages</A>?
 </BODY>
</HTML>

the relative URI "../cages/birds.gif" would resolve to:

http://www.aviary.com/cages/birds.gif

12.4.1 Resolving relative URIs

User agents must calculate the base URI for resolving relative URIs
according to [RFC1808], section 3. The following describes how [RFC1808]
applies specifically to HTML.

User agents must calculate the base URI according to the following
precedences (highest priority to lowest):

  1. The base URI is set by the BASE element.
  2. The base URI is given by meta data discovered during a protocol
     interaction, such as an HTTP header (see [RFC2068]).
  3. By default, the base URI is that of the current document. Not all HTML
     documents have a base URI (e.g., a valid HTML document may appear in an
     email and may not be designated by a URI). Such HTML documents are
     considered erroneous if they contain relative URIs and rely on a
     default base URI.

Additionally, the OBJECT and APPLET elements define attributes that take
precedence over the value set by the BASE element. Please consult the
definitions of these elements for more information about URI issues specific
to them.

Link elements specified by HTTP headers are handled exactly as LINK elements
that appear explicitly in a document.

                       13 Objects, Images, and Applets

Contents

  1. Introduction to objects, images, and applets
  2. Including an image: the IMG element
  3. Generic inclusion: the OBJECT element
       1. Rules for rendering objects
       2. Object initialization: the PARAM element
       3. Global naming schemes for objects
       4. Object declarations and instantiations
  4. Including an applet: the APPLET element
  5. Notes on embedded documents
  6. Image maps
       1. Client-side image maps: the MAP and AREA elements
             + Client-side image map examples
       2. Server-side image maps
  7. Visual presentation of images, objects, and applets
       1. Width and height
       2. White space around images and objects
       3. Borders
       4. Alignment
  8. How to specify alternate text

13.1 Introduction to objects, images, and applets

HTML's multimedia features allow authors to include images, applets
(programs that are automatically downloaded and run on the user's machine),
video clips, and other HTML documents in their pages.

For example, to include a PNG image in a document, authors may write:

<BODY>
<P>Here's a closeup of the Grand Canyon:
<OBJECT data="canyon.png" type="image/png">
This is a <EM>closeup</EM> of the Grand Canyon.
</OBJECT>
</BODY>

Previous versions of HTML allowed authors to include images (via IMG) and
applets (via APPLET). These elements have several limitations:

   * They fail to solve the more general problem of how to include new and
     future media types.
   * The APPLET element only works with Java-based applets. This element is
     deprecated in favor of OBJECT.
   * They pose accessibility problems.

To address these issues, HTML 4.0 introduces the OBJECT element, which
offers an all-purpose solution to generic object inclusion. The OBJECT
element allows HTML authors to specify everything required by an object for
its presentation by a user agent: source code, initial values, and run-time
data. In this specification, the term "object" is used to describe the
things that people want to place in HTML documents; other commonly used
terms for these things are: applets, plug-ins, media handlers, etc.

The new OBJECT element thus subsumes some of the tasks carried out by
existing elements. Consider the following chart of functionalities:

   Type of inclusion     Specific element    Generic element
 Image                 IMG                   OBJECT
 Applet                APPLET (Deprecated.)  OBJECT
 Another HTML document IFRAME                OBJECT

The chart indicates that each type of inclusion has a specific and a general
solution. The generic OBJECT element will serve as the solution for
implementing future media types.

To include images, authors may use the OBJECT element or the IMG element.

To include applets, authors should use the OBJECT element as the APPLET
element is deprecated.

To include one HTML document in another, authors may use either the new
IFRAME element or the OBJECT element. In both cases, the embedded document
remains independent of the main document. Visual user agents may present the
embedded document in a distinct window within the main document. Please
consult the notes on embedded documents for a comparison of OBJECT and
IFRAME for document inclusion.

Images and other included objects may have hyperlinks associated with them,
both through the standard linking mechanisms, but also via image maps. An
image map specifies active geometric regions of an included object and
assigns a link to each region. When activated, these links may cause a
document to be retrieved, may run a program on the server, etc.

In the following sections, we discuss the various mechanisms available to
authors for multimedia inclusions and creating image maps for those
inclusions.

13.2 Including an image: the IMG element

<!-- To avoid problems with text-only UAs as well as
   to make image content understandable and navigable
   to users of non-visual UAs, you need to provide
   a description with ALT, and avoid server-side image maps -->
<!ELEMENT IMG - O EMPTY                -- Embedded image -->
<!ATTLIST IMG
  %attrs;                              -- %coreattrs, %i18n, %events --
  src         %URI;          #REQUIRED -- URI of image to embed --
  alt         %Text;         #REQUIRED -- short description --
  longdesc    %URI;          #IMPLIED  -- link to long description
                                          (complements alt) --
  height      %Length;       #IMPLIED  -- override height --
  width       %Length;       #IMPLIED  -- override width --
  usemap      %URI;          #IMPLIED  -- use client-side image map --
  ismap       (ismap)        #IMPLIED  -- use server-side image map --
  >

Start tag: required, End tag: forbidden

Attribute definitions

src = uri [CT]
     This attribute specifies the location of the image resource. Examples
     of widely recognized image formats include GIF, JPEG, and PNG.
longdesc = uri [CT]
     This attribute specifies a link to a long description of the image.
     This description should supplement the short description provided using
     the alt attribute. When the image has an associated image map, this
     attribute should provide information about the image map's contents.
     This is particularly important for server-side image maps.

Attributes defined elsewhere

   * id, class (document-wide identifiers)
   * alt (alternate text)
   * lang (language information), dir (text direction)
   * title (element title)
   * style (inline style information)
   * onclick, ondblclick, onmousedown, onmouseup, onmouseover, onmousemove,
     onmouseout, onkeypress, onkeydown, onkeyup (intrinsic events)
   * ismap, usemap (client side image maps)
   * align, width, height, border, hspace, vspace (visual presentation of
     objects, images, and applets)

The IMG element embeds an image in the current document at the location of
the element's definition. The IMG element has no content; it is usually
replaced inline by the image designated by the src attribute, the exception
being for left or right-aligned images that are "floated" out of line.

In an earlier example, we defined a link to a family photo. Here, we insert
the photo directly into the current document:

<BODY>
<P>I just returned from vacation! Here's a photo of my family at the lake:
<IMG src="http://www.somecompany.com/People/Ian/vacation/family.png"
     alt="A photo of my family at the lake.">
</BODY>

This inclusion may also be achieved with the OBJECT element as follows:

<BODY>
<P>I just returned from vacation! Here's a photo of my family at the lake:
<OBJECT data="http://www.somecompany.com/People/Ian/vacation/family.png"
        type="image/png">
A photo of my family at the lake.
</OBJECT>
</BODY>

The alt attribute specifies alternate text that is rendered when the image
cannot be displayed (see below for information on how to specify alternate
text ). User agents must render alternate next when they cannot support
images, they cannot support a certain image type or when they are configured
not to display images.

The following example shows how the longdesc attribute can be used to link
to a richer description:

<BODY>
<P>
<IMG src="sitemap.gif"
     alt="HP Labs Site Map"
     longdesc="sitemap.html">
</BODY>

The alt attribute provides a short description of the image. This should be
sufficient to allow users to decide whether they want to follow the link
given by the longdesc attribute to the longer description, here
"sitemap.html".

Please consult the section on the visual presentation of objects, images,
and applets for information about image size, alignment, and borders.

13.3 Generic inclusion: the OBJECT element

<!ELEMENT OBJECT - - (PARAM | %flow;)*
 -- generic embedded object -->
<!ATTLIST OBJECT
  %attrs;                              -- %coreattrs, %i18n, %events --
  declare     (declare)      #IMPLIED  -- declare but don't instantiate flag --
  classid     %URI;          #IMPLIED  -- identifies an implementation --
  codebase    %URI;          #IMPLIED  -- base URI for classid, data, archive--
  data        %URI;          #IMPLIED  -- reference to object's data --
  type        %ContentType;  #IMPLIED  -- content type for data --
  codetype    %ContentType;  #IMPLIED  -- content type for code --
  archive     %URI;          #IMPLIED  -- space separated archive list --
  standby     %Text;         #IMPLIED  -- message to show while loading --
  height      %Length;       #IMPLIED  -- override height --
  width       %Length;       #IMPLIED  -- override width --
  usemap      %URI;          #IMPLIED  -- use client-side image map --
  name        CDATA          #IMPLIED  -- submit as part of form --
  tabindex    NUMBER         #IMPLIED  -- position in tabbing order --
  >

Start tag: required, End tag: required

Attribute definitions

classid = uri [CT]
     This attribute may be used to specify the location of an object's
     implementation via a URI. It may be used together with, or as an
     alternative to the data attribute, depending on the type of object
     involved.
codebase = uri [CT]
     This attribute specifies the base path used to resolve relative URIs
     specified by the classid, data, and archive attributes. When absent,
     its default value is the base URI of the current document.
codetype = content-type [CI]
     This attribute specifies the content type of data expected when
     downloading the object specified by classid. This attribute is optional
     but recommended when classid is specified since it allows the user
     agent to avoid loading information for unsupported content types. When
     absent, it defaults to the value of the type attribute.
data = uri [CT]
     This attribute may be used to specify the location of the object's
     data, for instance image data for objects defining images, or more
     generally, a serialized form of an object which can be used to recreate
     it. If given as a relative URI, it should be interpreted relative to
     the codebase attribute.
type = content-type [CI]
     This attribute specifies the content type for the data specified by
     data. This attribute is optional but recommended when data is specified
     since it allows the user agent to avoid loading information for
     unsupported content types.
archive = uri list [CT]
     This attribute may be used to specify a space-separated list of URIs
     for archives containing resources relevant to the object, which may
     include the resources specified by the classid and data attributes.
     Preloading archives will generally result in reduced load times for
     objects. Archives specified as relative URIs should be interpreted
     relative to the codebase attribute.
declare [CI]
     When present, this boolean attribute makes the current OBJECT
     definition a declaration only. The object must be instantiated by a
     subsequent OBJECT definition referring to this declaration.
standby = text [CS]
     This attribute specifies a message that a user agent may render while
     loading the object's implementation and data.

Attributes defined elsewhere

   * id, class (document-wide identifiers)
   * lang (language information), dir (text direction)
   * title (element title)
   * style (inline style information)
   * onclick, ondblclick, onmousedown, onmouseup, onmouseover, onmousemove,
     onmouseout, onkeypress, onkeydown, onkeyup (intrinsic events)
   * tabindex (tabbing navigation)
   * usemap (client side image maps)
   * name (form submission)
   * align, width, height, border, hspace, vspace (visual presentation of
     objects, images, and applets)

Most user agents have built-in mechanisms for rendering common data types
such as text, GIF images, colors, fonts, and a handful of graphic elements.
To render data types they don't support natively, user agents generally run
external applications. The OBJECT element allows authors to control whether
data should be rendered externally or by some program, specified by the
author, that renders the data within the user agent.

In the most general case, an author may need to specify three types of
information:

   * The implementation of the included object. For instance, if the
     included object is a clock applet, the author must indicate the
     location of the applet's executable code.
   * The data to be rendered. For instance, if the included object is a
     program that renders font data, the author must indicate the location
     of that data.
   * Additional values required by the object at run-time. For example, some
     applets may require initial values for parameters.

The OBJECT element allows authors to specify all three types of data, but
authors may not have to specify all three at once. For example, some objects
may not require data (e.g., a self-contained applet that performs a small
animation). Others may not require run-time initialization. Still others may
not require additional implementation information, i.e., the user agent
itself may already know how to render that type of data (e.g., GIF images).

Authors specify an object's implementation and the location of the data to
be rendered via the OBJECT element. To specify run-time values, however,
authors use the PARAM element, which is discussed in the section on object
initialization.

The OBJECT element may also appear in the content of the HEAD element. Since
user agents generally do not render elements in the HEAD, authors should
ensure that any OBJECT elements in the HEAD do not specify content that may
be rendered. Please consult the section on sharing frame data for an example
of including the OBJECT element in the HEAD element.

Please consult the section on form controls for information about OBJECT
elements in forms.

13.3.1 Rules for rendering objects

A user agent must interpret an OBJECT element according to the following
precedence rules:

  1. The user agent must first try to render the object. It should not
     render the element's contents, but it must examine them in case the
     element contains any direct children that are PARAM elements (see
     object initialization) or MAP elements (see client-side image maps).
  2. If the user agent is not able to render the object for whatever reason
     (configured not to, lack of resources, wrong architecture, etc.), it
     must try to render its contents.

Authors should not include content in OBJECT elements that appear in the
HEAD element.

In the following example, we insert an analog clock applet in a document via
the OBJECT element. The applet, written in the Python language, requires no
additional data or run-time values. The classid attribute specifies the
location of the applet:


<P><OBJECT classid="http://www.miamachina.it/analogclock.py">
</OBJECT>

Note that the clock will be rendered as soon as the user agent interprets
this OBJECT declaration. It is possible to delay rendering of an object by
first declaring the object (described below).

Authors should complete this declaration by including alternate text as the
contents of OBJECT in case the user agent cannot render the clock.


<P><OBJECT classid="http://www.miamachina.it/analogclock.py">
An animated clock.
</OBJECT>

One significant consequence of the OBJECT element's design is that it offers
a mechanism for specifying alternate object renderings; each embedded OBJECT
declaration may specify alternate content types. If a user agent cannot
render the outermost OBJECT, it tries to render the contents, which may be
another OBJECT element, etc.

In the following example, we embed several OBJECT declarations to illustrate
how alternate renderings work. A user agent will attempt to render the first
OBJECT element it can, in the following order: (1) an Earth applet written
in the Python language, (2) an MPEG animation of the Earth, (3) a GIF image
of the Earth, (4) alternate text.

<P>                 <!-- First, try the Python applet -->
<OBJECT title="The Earth as seen from space"
        classid="http://www.observer.mars/TheEarth.py">
                    <!-- Else, try the MPEG video -->
  <OBJECT data="TheEarth.mpeg" type="application/mpeg">
                    <!-- Else, try the GIF image -->
    <OBJECT data="TheEarth.gif" type="image/gif">
                    <!-- Else render the text -->
     The <STRONG>Earth</STRONG> as seen from space.
    </OBJECT>
  </OBJECT>
</OBJECT>

The outermost declaration specifies an applet that requires no data or
initial values. The second declaration specifies an MPEG animation and,
since it does not define the location of an implementation to handle MPEG,
relies on the user agent to handle the animation. We also set the type
attribute so that a user agent that knows it cannot render MPEG will not
bother to retrieve "TheEarth.mpeg" from the network. The third declaration
specifies the location of a GIF file and furnishes alternate text in case
all other mechanisms fail.

Inline vs. external data. Data to be rendered may be supplied in two ways:
inline and from an external resource. While the former method will generally
lead to faster rendering, it is not convenient when rendering large
quantities of data.

Here's an example that illustrates how inline data may be fed to an OBJECT:

<P>
<OBJECT id="clock1"
        classid="clsid:663C8FEF-1EF9-11CF-A3DB-080036F12502"
        data="data:application/x-oleobject;base64, ...base64 data...">
    A clock.
</OBJECT>

Please consult the section on the visual presentation of objects, images,
and applets for information about object size, alignment, and borders.

13.3.2 Object initialization: the PARAM element

<!ELEMENT PARAM - O EMPTY              -- named property value -->
<!ATTLIST PARAM
  id          ID             #IMPLIED  -- document-wide unique id --
  name        CDATA          #REQUIRED -- property name --
  value       CDATA          #IMPLIED  -- property value --
  valuetype   (DATA|REF|OBJECT) DATA   -- How to interpret value --
  type        %ContentType;  #IMPLIED  -- content type for value
                                          when valuetype=ref --
  >

Start tag: required, End tag: forbidden

Attribute definitions

name = cdata
     This attribute defines the name of a run-time parameter, assumed to be
     known by the inserted object. Whether the property name is
     case-sensitive depends on the specific object implementation.
value = cdata
     This attribute specifies the value of a run-time parameter specified by
     name. Property values have no meaning to HTML; their meaning is
     determined by the object in question.
valuetype = data|ref|object [CI]
     This attribute specifies the type of the value attribute. Possible
     values:
        o data: This is default value for the attribute. It means that the
          value specified by value will be evaluated and passed to the
          object's implementation as a string.
        o ref: The value specified by value is a URI that designates a
          resource where run-time values are stored. This allows support
          tools to identify URIs given as parameters. The URI must be passed
          to the object as is, i.e., unresolved.
        o object: The value specified by value is an identifier that refers
          to an OBJECT declaration in the same document. The identifier must
          be the value of the id attribute set for the declared OBJECT
          element.
type = content-type [CI]
     This attribute specifies the content type of the resource designated by
     the value attribute only in the case where valuetype is set to "ref".
     This attribute thus specifies for the user agent, the type of values
     that will be found at the URI designated by value.

Attributes defined elsewhere

   * id (document-wide identifiers)

PARAM elements specify a set of values that may be required by an object at
run-time. Any number of PARAM elements may appear in the content of an
OBJECT or APPLETelement, in any order, but must be placed at the start of
the content of the enclosing OBJECT or APPLET element.

The syntax of names and values is assumed to be understood by the object's
implementation. This document does not specify how user agents should
retrieve name/value pairs nor how they should interpret parameter names that
appear twice.

We return to the clock example to illustrate the use of PARAM: suppose that
the applet is able to handle two run-time parameters that define its initial
height and width. We can set the initial dimensions to 40x40 pixels with two
PARAM elements.


<P><OBJECT classid="http://www.miamachina.it/analogclock.py">
<PARAM name="height" value="40" valuetype="data">
<PARAM name="width" value="40" valuetype="data">
This user agent cannot render Python applications.
</OBJECT>

In the following example, run-time data for the object's "Init_values"
parameter is specified as an external resource (a GIF file). The value of
the valuetype attribute is thus set to "ref" and the value is a URI
designating the resource.

<P><OBJECT classid="http://www.gifstuff.com/gifappli"
       standby="Loading Elvis...">
<PARAM name="Init_values"
       value="./images/elvis.gif">
       valuetype="ref">
</OBJECT>

Note that we have also set the standby attribute so that the user agent may
display a message while the rendering mechanism loads.

When an OBJECT element is rendered, user agents must search the content for
only those PARAM elements that are direct children and "feed" them to the
OBJECT.

Thus, in the following example, if "obj1" is rendered, "param1" applies to
"obj1" (and not "obj2"). If "obj1" is not rendered and "obj2" is, "param1"
is ignored, and "param2" applies to "obj2". If neither OBJECT is rendered,
neither PARAM applies.

<P>
<OBJECT id="obj1">
   <PARAM name="param1">
   <OBJECT id="obj2">
      <PARAM name="param2">
   </OBJECT>
</OBJECT>

13.3.3 Global naming schemes for objects

The location of an object's implementation is given by a URI. As we
discussed in the introduction to URIs, the first segment of an absolute URI
specifies the naming scheme used to transfer the data designated by the URI.
For HTML documents, this scheme is frequently "http". Some applets might
employ other naming schemes. For instance, when specifying a Java applet,
authors may use URIs that begin with "java" and for ActiveX applets, authors
may use "clsid".

In the following example, we insert a Java applet into an HTML document.

<P><OBJECT classid="java:program.start">
</OBJECT>

By setting the codetype attribute, a user agent can decide whether to
retrieve the Java application based on its ability to do so.

<OBJECT codetype="application/java-archive"
        classid="java:program.start">
</OBJECT>

Some rendering schemes require additional information to identify their
implementation and must be told where to find that information. Authors may
give path information to the object's implementation via the codebase
attribute.

<OBJECT codetype="application/java-archive"
        classid="java:program.start">
        codebase="http://foooo.bar.com/java/myimplementation/"
</OBJECT>

The following example specifies (with the classid attribute) an ActiveX
object via a URI that begins with the naming scheme "clsid". The data
attribute locates the data to render (another clock).

<P><OBJECT classid="clsid:663C8FEF-1EF9-11CF-A3DB-080036F12502"
        data="http://www.acme.com/ole/clock.stm">
This application is not supported.
</OBJECT>

13.3.4 Object declarations and instantiations

The preceding examples have only illustrated isolated object definitions.
When a document is to contain more than one instance of the same object, it
is possible to separate the declaration of the object from its
instantiations. Doing so has several advantages:

   * Data may be retrieved from the network by the user agent one time
     (during the declaration) and reused for each instantiation.
   * It is possible to instantiate an object from a location other than the
     object's declaration, for example, from a link.
   * It is possible to specify objects as run-time data for other objects.

To declare an object so that it is not executed when read by the user agent,
set the boolean declare attribute in the OBJECT element. At the same time,
authors must identify the declaration by setting the id attribute in the
OBJECT element to a unique value. Later instantiations of the object will
refer to this identifier.

A declared OBJECT must appear in a document before the first instance of
that OBJECT.

An object defined with the declare attribute is instantiated every time an
element that refers to that object requires it to be rendered (e.g., a link
that refers to it is activated, an object that refers to it is activated,
etc.).

In the following example, we declare an OBJECT and cause it so be
instantiated by referring to it from a link. Thus, the object can be
activated by clicking on some highlighted text, for example.

<P><OBJECT declare
        id="earth.declaration"
        data="TheEarth.mpeg"
        type="application/mpeg">
   The <STRONG>Earth</STRONG> as seen from space.
</OBJECT>
...later in the document...
<P>A neat <A href="#earth.declaration"> animation of The Earth!</A>

The following example illustrates how to specify run-time values that are
other objects. In this example, we send text (a poem, in fact) to a
hypothetical mechanism for viewing poems. The object recognizes a run-time
parameter named "font" (say, for rendering the poem text in a certain font).
The value for this parameter is itself an object that inserts (but does not
render) the font object. The relationship between the font object and the
poem viewer object is achieved by (1) assigning the id "tribune" to the font
object declaration and (2) referring to it from the PARAM element of the
poem viewer object (with valuetype and value).

<P><OBJECT declare
     id="tribune"
     type="application/x-webfont"
     data="tribune.gif">
</OBJECT>
...view the poem in KublaKhan.txt here...
<P><OBJECT classid="http://foo.bar.com/poem_viewer"
           data="KublaKhan.txt">
<PARAM name="font" valuetype="object" value="#tribune">
<P>You're missing a really cool poem viewer ...
</OBJECT>

User agents that don't support the declare attribute must render the
contents of the OBJECT declaration.

13.4 Including an applet: the APPLET element

APPLET is deprecated (with all its attributes) in favor of OBJECT.

See the Transitional DTD for the formal definition.

Attribute definitions

codebase = uri [CT]
     This attribute specifies the base URI for the applet. If this attribute
     is not specified, then it defaults the same base URI as for the current
     document. Values for this attribute may only refer to subdirectories of
     the directory containing the current document.
code = cdata [CS]
     This attribute specifies either the name of the class file that
     contains the applet's compiled applet subclass or the path to get the
     class, including the class file itself. It is interpreted with respect
     to the applet's codebase. One of code or object must be present.
name = cdata [CS]
     This attribute specifies a name for the applet instance, which makes it
     possible for applets on the same page to find (and communicate with)
     each other.
archive = uri-list [CT]
     This attribute specifies a comma-separated list of URIs for archives
     containing classes and other resources that will be "preloaded". The
     classes are loaded using an instance of an AppletClassLoader with the
     given codebase. Relative URIs for archives are interpreted with respect
     to the applet's codebase. Preloading resources can significantly
     improve the performance of applets.
object = cdata [CS]
     This attribute names a resource containing a serialized representation
     of an applet's state. It is interpreted relative to the applet's
     codebase. The serialized data contains the applet's class name but not
     the implementation. The class name is used to retrieve the
     implementation from a class file or archive.

     When the applet is "deserialized" the start() method is invoked but not
     the init() method. Attributes valid when the original object was
     serialized are not restored. Any attributes passed to this APPLET
     instance will be available to the applet. Authors should use this
     feature with extreme caution. An applet should be stopped before it is
     serialized.

     Either code or object must be present. If both code and object are
     given, it is an error if they provide different class names.

width = length [CI]
     This attribute specifies the initial width of the applet's display area
     (excluding any windows or dialogs that the applet creates).
height = length [CI]
     This attribute specifies the initial height of the applet's display
     area (excluding any windows or dialogs that the applet creates).

Attributes defined elsewhere

   * id, class (document-wide identifiers)
   * title (element title)
   * style (inline style information)
   * alt (alternate text)
   * align, hspace, vspace (visual presentation of objects, images, and
     applets)

This element, supported by all Java-enabled browsers, allows designers to
embed a Java applet in an HTML document. It has been deprecated in favor of
the OBJECT element.

The content of the APPLET acts as alternate information for user agents that
don't support this element or are currently configured not to support
applets. User agents must ignore the content otherwise.

DEPRECATED EXAMPLE:
In the following example, the APPLET element includes a Java applet in the
document. Since no codebase is supplied, the applet is assumed to be in the
same directory as the current document.

<APPLET code="Bubbles.class" width="500" height="500">
Java applet that draws animated bubbles.
</APPLET>

This example may be rewritten as follows with OBJECT as follows:

<P><OBJECT codetype="application/java"
        classid="java:Bubbles.class"
        width="500" height="500">
Java applet that draws animated bubbles.
</OBJECT>

Initial values may be supplied to the applet via the PARAM element.

DEPRECATED EXAMPLE:
The following sample Java applet:

<APPLET code="AudioItem" width="15" height="15">
<PARAM name="snd" value="Hello.au|Welcome.au">
Java applet that plays a welcoming sound.
</APPLET>

may be rewritten as follows with OBJECT:

<OBJECT codetype="application/java"
        classid="AudioItem"
        width="15" height="15">
<PARAM name="snd" value="Hello.au|Welcome.au">
Java applet that plays a welcoming sound.
</OBJECT>

13.5 Notes on embedded documents

Sometimes, rather than linking to a document, an author may want to embed it
directly into a primary HTML document. Authors may use either the IFRAME
element or the OBJECT element for this purpose, but the elements differ in
some ways. Not only do the two elements have different content models, the
IFRAME element may be a target frame (see the section on specifying target
frame information for details) and may be "selected" by a user agent as the
focus for printing, viewing HTML source, etc. User agents may render
selected frames elements in ways that distinguish them from unselected
frames (e.g., by drawing a border around the selected frame).

An embedded document is entirely independent of the document in which it is
embedded. For instance, relative URIs within the embedded document resolve
according to the base URI of the embedded document, not that of the main
document. An embedded document is only rendered within another document
(e.g., in a subwindow); it remains otherwise independent.

For instance, the following line embeds the contents of embed_me.html at the
location where the OBJECT definition occurs.

...text before...
<OBJECT data="embed_me.html">
Warning: embed_me.html could not be embedded.
</OBJECT>
...text after...

Recall that the contents of OBJECT must only be rendered if the file
specified by the data attribute cannot be loaded.

The behavior of a user agent in cases where a file includes itself is not
defined.

13.6 Image maps

Image maps allow authors to specify regions of an image or object and assign
a specific action to each region (e.g., retrieve a document, run a program,
etc.) When the region is activated by the user, the action is executed.

An image map is created by associating an object with a specification of
sensitive geometric areas on the object.

There are two types of image maps:

   * Client-side. When a user activates a region of a client-side image map
     with a mouse, the pixel coordinates are interpreted by the user agent.
     The user agent selects a link that was specified for the activated
     region and follows it.
   * Server-side. When a user activates a region of a server-side image map
     with a mouse, the pixel coordinates of the click are sent to the
     server-side agent specified by the href attribute of the A element. The
     server-side agent interprets the coordinates and performs some action.

Client-side image maps are preferred over server-side image maps for at
least two reasons: they are accessible to people browsing with non-graphical
user agents and they offer immediate feedback as to whether or not the
pointer is over an active region.

13.6.1 Client-side image maps: the MAP and AREA elements

<!ELEMENT MAP - - ((%block;)+ | AREA+) -- client-side image map -->
<!ATTLIST MAP
  %attrs;                              -- %coreattrs, %i18n, %events --
  name        CDATA          #REQUIRED -- for reference by usemap --
  >

Start tag: required, End tag: required

<!ELEMENT AREA - O EMPTY               -- client-side image map area -->
<!ATTLIST AREA
  %attrs;                              -- %coreattrs, %i18n, %events --
  shape       %Shape;        rect      -- controls interpretation of coords --
  coords      %Coords;       #IMPLIED  -- comma separated list of lengths --
  href        %URI;          #IMPLIED  -- URI for linked resource --
  nohref      (nohref)       #IMPLIED  -- this region has no action --
  alt         %Text;         #REQUIRED -- short description --
  tabindex    NUMBER         #IMPLIED  -- position in tabbing order --
  accesskey   %Character;    #IMPLIED  -- accessibility key character --
  onfocus     %Script;       #IMPLIED  -- the element got the focus --
  onblur      %Script;       #IMPLIED  -- the element lost the focus --
  >

Start tag: required, End tag: forbidden

MAP attribute definitions

name = cdata [CI]
     This attribute assigns a name to the image map defined by a MAP
     element.

AREA attribute definitions

shape = default|rect|circle|poly [CI]
     This attribute specifies the shape of a region. Possible values:
        o default: Specifies the entire region.
        o rect: Define a rectangular region.
        o circle: Define a circular region.
        o poly: Define a polygonal region.
coords = coordinates [CN]
     This attribute specifies the position a shape on the screen. The number
     and order of values depends on the shape being defined. Possible
     combinations:
        o rect: left-x, top-y, right-x, bottom-y.
        o circle: center-x, center-y, radius. Note. When the radius value is
          a percentage value, user agents should calculate the final radius
          value based on the associated object's width and height. The
          radius should be the smaller value of the two.
        o poly: x1, y1, x2, y2, ..., xN, yN.

     Coordinates are relative to the top, left corner of the object. All
     values are lengths. All values are separated by commas.
nohref [CI]
     When set, this boolean attribute specifies that a region has no
     associated link.

Attribute to associate an image map with an element

usemap = uri [CT]
     This attribute associates an image map with an element. The image map
     is defined by a MAP element. The value of usemap must match the value
     of the name attribute of the associated MAP element.

Attributes defined elsewhere

   * id, class (document-wide identifiers)
   * lang (language information), dir (text direction)
   * title (element title)
   * style (inline style information)
   * name (submitting objects with forms)
   * alt (alternate text)
   * href ( anchor reference) target (frame target information)
   * tabindex (tabbing navigation)
   * accesskey (access keys)
   * shape (image maps)
   * onclick, ondblclick, onmousedown, onmouseup, onmouseover, onmousemove,
     onmouseout, onkeypress, onkeydown, onkeyup, onfocus, onblur (intrinsic
     events)

The MAP element specifies a client-side image map that may be associated
with one or more elements (IMG, OBJECT, or INPUT). An image map is
associated with an element via the element's usemap attribute.

The presence of the usemap attribute for an OBJECT implies that the object
being included is an image. Furthermore, when the OBJECT element has an
associated client-side image map, user agents may implement user interaction
with the OBJECT solely in terms of the client-side image map. This allows
user agents (such as an audio browser or robot) to interact with the OBJECT
without having to process it; the user agent may even elect not to retrieve
(or process) the object. When an OBJECT has an associated image map, authors
should not expect that the object will be retrieved or processed by every
user agent.

Each MAP element may contain either one of the following:

  1. One or more AREA elements. These elements have no content but specify
     the geometric regions of the image map and the link associated with
     each region. Note that when this method is used, the MAP has no
     rendered content. Therefore, authors must provide alternate text for
     each AREA with the alt attribute (see below for information on how to
     specify alternate text).
  2. Block-level content. This content should include A elements that
     specify the geometric regions of the image map and the link associated
     with each region. Note that when this method is used, the MAP element
     content may be rendered by the user agent. Authors should use this
     method to create more accessible documents.

If two or more defined regions overlap, the region-defining element that
appears earliest in the document takes precedence (i.e., responds to user
input).

User agents and authors should offer textual alternates to graphical image
maps for cases when graphics are not available or the user cannot access
them. For example, user agents may use alt text to create textual links in
place of a graphical image map. Such links may be activated in a variety of
ways (keyboard, voice activation, etc.).

Note. MAP is not backwards compatible with HTML 2.0 user agents.

Client-side image map examples

In the following example, we create a client-side image map for the OBJECT
element. We do not want to render the image map's contents when the OBJECT
is rendered, so we "hide" the MAP element within the OBJECT element's
content. Consequently, the MAP element's contents will only be rendered if
the OBJECT cannot be rendered.

<HTML>
   <HEAD>
      <TITLE>The cool site!</TITLE>
   </HEAD>
   <BODY>
     <P><OBJECT data="navbar1.gif" type="image/gif" usemap="#map1">
     <MAP name="map1">
       <P>Navigate the site:
       <A href="guide.html" shape="rect" coords="0,0,118,28">Access Guide</a> |
       <A href="shortcut.html" shape="rect" coords="118,0,184,28">Go</A> |
       <A href="search.html" shape="circle" coords="184,200,60">Search</A> |
       <A href="top10.html" shape="poly" coords="276,0,373,28,50,50,276,0">Top Ten</A><
     </MAP>
     </OBJECT>
   </BODY>
</HTML>

We may want to render the image map's contents even when a user agent can
render the OBJECT. For instance, we may want to associate an image map with
an OBJECT element and include a text navigation bar at the bottom of the
page. To do so, we define the MAP element outside the OBJECT:

<HTML>
   <HEAD>
      <TITLE>The cool site!</TITLE>
   </HEAD>
   <BODY>
     <P><OBJECT data="navbar1.gif" type="image/gif" usemap="#map1">
     </OBJECT>

     ...the rest of the page here...

     <MAP name="map1">
       <P>Navigate the site:
       <A href="guide.html" shape="rect" coords="0,0,118,28">Access Guide</a> |
       <A href="shortcut.html" shape="rect" coords="118,0,184,28">Go</A> |
       <A href="search.html" shape="circle" coords="184,200,60">Search</A> |
       <A href="top10.html" shape="poly" coords="276,0,373,28,50,50,276,0">Top Ten</A>
     </MAP>
   </BODY>
</HTML>

In the following example, we create a similar image map, this time using the
AREA element. Note the use of alt text:

<P><OBJECT data="navbar1.gif" type="image/gif" usemap="#map1">
   <P>This is a navigation bar.
   </OBJECT>

<MAP name="map1">
 <AREA href="guide.html"
          alt="Access Guide"
          shape="rect"
          coords="0,0,118,28">
 <AREA href="search.html"
          alt="Search"
          shape="rect"
          coords="184,0,276,28">
 <AREA href="shortcut.html"
          alt="Go"
          shape="circle"
          coords="184,200,60">
 <AREA href="top10.html"
          alt="Top Ten"
          shape="poly"
          coords="276,0,373,28,50,50,276,0">
</MAP>

Here is a similar version using the IMG element instead of OBJECT (with the
same MAP declaration):

<P><IMG src="navbar1.gif" usemap="#map1" alt="navigation bar">

The following example illustrates how image maps may be shared.

Nested OBJECT elements are useful for providing fallbacks in case a user
agent doesn't support certain formats. For example:

<P>
<OBJECT data="navbar.png" type="image/png">
  <OBJECT data="navbar.gif" type="image/gif">
    text describing the image...
  </OBJECT>
</OBJECT>

If the user agent doesn't support the PNG format, it tries to render the GIF
image. If it doesn't support GIF (e.g., it's a speech-based user agent), it
defaults to the text description provided as the content of the inner OBJECT
element. When OBJECT elements are nested this way, authors may share image
maps among them:

<P>
<OBJECT data="navbar.png" type="image/png" usemap="#map1">
  <OBJECT data="navbar.gif" type="image/gif" usemap="#map1">
     <MAP name="map1">
     <P>Navigate the site:
      <A href="guide.html" shape="rect" coords="0,0,118,28">Access Guide</a> |
      <A href="shortcut.html" shape="rect" coords="118,0,184,28">Go</A> |
      <A href="search.html" shape="circle" coords="184,200,60">Search</A> |
      <A href="top10.html" shape="poly" coords="276,0,373,28,50,50,276,0">Top Ten</A>
     </MAP>
  </OBJECT>
</OBJECT>

The following example illustrates how anchors may be specified to create
inactive zones within an image map. The first anchor specifies a small
circular region with no associated link. The second anchor specifies a
larger circular region with the same center coordinates. Combined, the two
form a ring whose center is inactive and whose rim is active. The order of
the anchor definitions is important, since the smaller circle must override
the larger circle.

<MAP name="map1">
<P>
<A shape="circle" coords="100,200,50">I'm inactive.</A>
<A href="outer-ring-link.html" shape="circle" coords="100,200,250">I'm active.</A>
</MAP>

Similarly, the nohref attribute for the AREA element declares that geometric
region has no associated link.

13.6.2 Server-side image maps

Server-side image maps may be interesting in cases where the image map is
too complicated for a client-side image map.

It is only possible to define a server-side image map for the IMG and INPUT
elements. In the case of IMG, the IMG must be enclosed by an A element. In
the case of INPUT, the INPUT must be of type "image". In both cases, the
boolean attribute ismap [CI] on the element must be set.

When the user activates the link by clicking on the image, the screen
coordinates are sent directly to the server where the document resides.
Screen coordinates are expressed as screen pixel values relative to the
image. For normative information about the definition of a pixel and how to
scale it, please consult [CSS1].

In the following example, the active region defines a server-side link.
Thus, a click anywhere on the image will cause the click's coordinates to be
sent to the server.

<P><A href="http://www.acme.com/cgi-bin/competition">
        <IMG src="game.gif" ismap alt="target"></A>

The location clicked is passed to the server as follows. The user agent
derives a new URI from the URI specified by the href attribute of the A
element, by appending `?' followed by the x and y coordinates, separated by
a comma. The link is then followed using the new URI. For instance, in the
given example, if the user clicks at the location x=10, y=27 then the
derived URI is "http://www.acme.com/cgi-bin/competition?10,27".

User agents that do not offer the user a means to select specific
coordinates (e.g., non-graphical user agents that rely on keyboard input,
speech-based user agents, etc.) should send the coordinates "0,0" to the
server when the link is activated.

13.7 Visual presentation of images, objects, and applets

All IMG and OBJECT attributes that concern visual alignment and presentation
have been deprecated in favor of style sheets.

13.7.1 Width and height

Attribute definitions

width = length [CN]
     Image and object width override.
height = length [CN]
     Image and object override.

When specified, the width and height attributes tell user agents to override
the natural image or object size in favor of these values.

When the object is an image, it is scaled. User agents should do their best
to scale an object or image to match the width and height specified by the
author. Note that lengths expressed as percentages are based on the
horizontal or vertical space currently available, not on the natural size of
the image, object, or applet.

The height and width attributes give user agents an idea of the size of an
image or object so that they may reserve space for it and continue rendering
the document while waiting for the image data.

13.7.2 White space around images and objects

The vspace and hspace attributes specify the amount of white space to be
inserted to the left and right (hspace) and above and below (vspace) an IMG,
APPLET, OBJECT. The default value for these attributes is not specified, but
is generally a small, non-zero length. Both attributes take values of type
length.

13.7.3 Borders

An image or object may be surrounded by a border (e.g., when a border is
specified by the user or when the image is the content of an A element).

Attribute definitions

border = pixels
     Deprecated. The border attribute specifies the width of this border in
     pixels. The default value for this attribute depends on the user agent.

13.7.4 Alignment

The align attribute specifies the position of an IMG, OBJECT, or APPLET with
respect to its context.

The following values for align concern the object's position with respect to
surrounding text:

   * bottom: means that the bottom of the object should be vertically
     aligned with the current baseline. This is the default value.
   * middle: means that the center of the object should be vertically
     aligned with the current baseline.
   * top: means that the top of the object should be vertically aligned with
     the top of the current text line.

Two other values, left and right, cause the image to float to the current
left or right margin. They are discussed in the section on floating objects.

Differing interpretations of align. User agents vary in their interpretation
of the align attribute. Some only take into account what has occurred on the
text line prior to the element, some take into account the text on both
sides of the element.

13.8 How to specify alternate text

Attribute definitions

alt = text [CS]
     For user agents that cannot display images, forms, or applets, this
     attribute specifies alternate text. The language of the alternate text
     is specified by the lang attribute.

Several non-textual elements (IMG, AREA, APPLET, and INPUT) require authors
to specify alternate text to serve as content when the element cannot be
rendered normally. Specifying alternate text assists users without graphic
display terminals, users whose browsers don't support forms, visually
impaired users, those who use speech synthesizers, those who have configured
their graphical user agents not to display images, etc.

The alt attribute must be specified for the IMG and AREA elements. It is
optional for the INPUT and APPLET elements.

While alternate text may be very helpful, it must be handled with care.
Authors should observe the following guidelines:

   * Do not specify irrelevant alternate text when including images intended
     to format a page, for instance, alt="red ball" would be inappropriate
     for an image that adds a red ball for decorating a heading or
     paragraph. In such cases, the alternate text should be the empty string
     (""). Authors are in any case advised to avoid using images to format
     pages; style sheets should be used instead.
   * Do not specify meaningless alternate text (e.g., "dummy text"). Not
     only will this frustrate users, it will slow down user agents that must
     convert text to speech or braille output.

Implementors should consult the section on generating alternate text for
information about how to handle cases of omitted alternate text.

Note. For more information about designing accessible HTML documents, please
consult [WAIGUIDE].

                               14 Style Sheets

Contents

  1. Introduction to style sheets
  2. Adding style to HTML
       1. Setting the default style sheet language
       2. Inline style information
       3. Header style information: the STYLE element
       4. Media types
  3. External style sheets
       1. Preferred and alternate style sheets
       2. Specifying external style sheets
  4. Cascading style sheets
       1. Media-dependent cascades
       2. Inheritance and cascading
  5. Hiding style data from user agents
  6. Linking to style sheets with HTTP headers

14.1 Introduction to style sheets

Style sheets represent a major breakthrough for Web page designers,
expanding their ability to improve the appearance of their pages. In the
scientific environments in which the Web was conceived, people are more
concerned with the content of their documents than the presentation. As
people from wider walks of life discovered the Web, the limitations of HTML
became a source of continuing frustration and authors were forced to
sidestep HTML's stylistic limitations. While the intentions have been good
-- to improve the presentation of Web pages -- the techniques for doing so
have had unfortunate side effects. These techniques work for some of the
people, some of the time, but not for all of the people, all of the time.
They include:

   * Using proprietary HTML extensions
   * Converting text into images
   * Using images for white space control
   * Use of tables for page layout
   * Writing a program instead of using HTML

These techniques considerably increase the complexity of Web pages, offer
limited flexibility, suffer from interoperability problems, and create
hardships for people with disabilities.

Style sheets solve these problems at the same time they supersede the
limited range of presentation mechanisms in HTML. Style sheets make it easy
to specify the amount of white space between text lines, the amount lines
are indented, the colors used for the text and the backgrounds, the font
size and style, and a host of other details.

For example, the following short CSS style sheet (stored in the file
"special.css"), sets the text color of a paragraph to green and surrounds it
with a solid red border:

P.special {
color : green;
border: solid red;
}

Authors may link this style sheet to their source HTML document with the
LINK element:

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0//EN"
   "http://www.w3.org/TR/REC-html40">
<HTML>
  <HEAD>
    <LINK href="special.css" rel="stylesheet" type="text/css">
  </HEAD>
  <BODY>
    <P class="special">This paragraph should have special green text.
  </BODY>
</HTML>

HTML 4.0 provides support for the following style sheet features:

Flexible placement of style information
     Placing style sheets in separate files makes them easy to reuse.
     Sometimes it's useful to include rendering instructions within the
     document to which they apply, either grouped at the start of the
     document, or in attributes of the elements throughout the body of the
     document. To make it easier to manage style on a site basis, this
     specification describes how to use HTTP headers to set the style sheets
     to be applied to a document.
Independence from specific style sheet languages
     This specification doesn't tie HTML to any particular style sheet
     language. This allows for a range of such languages to be used, for
     instance simple ones for the majority of users and much more complex
     ones for the minority of users with highly specialized needs. The
     examples included below all use the CSS (Cascading Style Sheets)
     language [CSS1], but other style sheet languages would be possible.
Cascading
     This is the capability provided by some style sheet languages such as
     CSS to allow style information from several sources to be blended
     together. These could be, for instance, corporate style guidelines,
     styles common to a group of documents, and styles specific to a single
     document. By storing these separately, style sheets can be reused,
     simplifying authoring and making more effective use of network caching.
     The cascade defines an ordered sequence of style sheets where rules in
     later sheets have greater precedence than earlier ones. Not all style
     sheet languages support cascading.
Media dependencies
     HTML allows authors to specify documents in a media-independent way.
     This allows users to access Web pages using a wide variety of devices
     and media, e.g., graphical displays for computers running Windows,
     Macintosh OS, and X11, devices for television sets, specially adapted
     phones and PDA-based portable devices, speech-based browsers, and
     braille-based tactile devices.

     Style sheets, by contrast, apply to specific media or media groups. A
     style sheet intended for screen use may be applicable when printing,
     but is of little use for speech-based browsers. This specification
     allows you to define the broad categories of media a given style sheet
     is applicable to. This allows user agents to avoid retrieving
     inappropriate style sheets. Style sheet languages may include features
     for describing media dependencies within the same style sheet.
Alternate styles
     Authors may wish to offer readers several ways to view a document. For
     instance, a style sheet for rendering compact documents with small
     fonts, or one that specifies larger fonts for increased legibility.
     This specification allows authors to specify a preferred style sheet as
     well as alternates that target specific users or media. User agents
     should give users the opportunity to select from among alternate style
     sheets or to switch off style sheets altogether.
Performance concerns
     Some people have voiced concerns over performance issues for style
     sheets. For instance, retrieving an external style sheet may delay the
     full presentation for the user. A similar situation arises if the
     document head includes a lengthy set of style rules.

     The current proposal addresses these issues by allowing authors to
     include rendering instructions within each HTML element. The rendering
     information is then always available by the time the user agent wants
     to render each element.

     In many cases, authors will take advantage of a common style sheet for
     a group of documents. In this case, distributing style rules throughout
     the document will actually lead to worse performance than using a
     linked style sheet, since for most documents, the style sheet will
     already be present in the local cache. The public availability of good
     style sheets will encourage this effect.

14.2 Adding style to HTML

Note. The sample default style sheet for HTML 4.0 that is included in [CSS2]
expresses generally accepted default style information for each element.
Authors and implementors alike might find this a useful resource.

HTML documents may contain style sheet rules directly in them or they may
import style sheets.

Any style sheet language may be used with HTML. A simple style sheet
language may suffice for the needs of most users, but other languages may be
more suited to highly specialized needs. This specification uses the style
language "Cascading Style Sheets" ([CSS1]), abbreviated CSS, for examples.

The syntax of style data depends on the style sheet language.

14.2.1 Setting the default style sheet language

Authors must specify the style sheet language of style information
associated with an HTML document.

Authors should use the META element to set the default style sheet language
for a document. For example, to set the default to CSS, authors should put
the following declaration in the HEAD of their documents:

<META http-equiv="Content-Style-Type" content="text/css">

The default style sheet language may also be set with HTTP headers. The
above META declaration is equivalent to the HTTP header:

Content-Style-Type: text/css

User agents should determine the default style sheet language for a document
according to the following steps (highest to lowest priority):

  1. If any META declarations specify the "Content-Style-Type", the last one
     in the character stream determines the default style sheet language.
  2. Otherwise, if any HTTP headers specify the "Content-Style-Type", the
     last one in the character stream determines the default style sheet
     language.
  3. Otherwise, the default style sheet language is "text/css".

Documents that include elements that set the style attribute but which don't
define a default style sheet language are incorrect. Authoring tools should
generate default style sheet language information (typically a META
declaration) so that user agents do not have to rely on a default of
"text/css".

14.2.2 Inline style information

Attribute definitions

style = style [CN]
     This attribute specifies style information for the current element.

style The style attribute specifies style information for a single element.
The style sheet language of inline style rules is given by the default style
sheet language. The syntax of style data depends on the style sheet
language.

This example sets color and font size information for the text in a specific
paragraph.

<P style="font-size: 12pt; color: fuchsia">Aren't style sheets wonderful?

In CSS, property declarations have the form "name : value" and are separated
by a semi-colon.

The style attribute may be used to apply a particular style to an individual
HTML element. If the style will be reused for several elements, authors
should use the STYLE element to regroup that information. For optimal
flexibility, authors should define styles in external style sheets.

14.2.3 Header style information: the STYLE element

<!ELEMENT STYLE - - %StyleSheet        -- style info -->
<!ATTLIST STYLE
  %i18n;                               -- lang, dir, for use with title --
  type        %ContentType;  #REQUIRED -- content type of style language --
  media       %MediaDesc;    #IMPLIED  -- designed for use with these media --
  title       %Text;         #IMPLIED  -- advisory title --
  >

Start tag: required, End tag: required

Attribute definitions

type = content-type [CI]
     This attribute specifies the style sheet language of the element's
     contents and overrides the default style sheet language. The style
     sheet language is specified as a content type (e.g., "text/css").
     Authors must supply a value for this attribute; there is no default
     value for this attribute.
media = media-descriptors [CI]
     This attribute specifies the intended destination medium for style
     information. It may be a single media descriptor or a comma-separated
     list. The default value for this attribute is "screen".

Attributes defined elsewhere

   * lang (language information), dir (text direction)

The STYLE element allows authors to put style sheet rules in the head of the
document. HTML permits any number of STYLE elements in the HEAD section of a
document.

User agents that don't support style sheets, or don't support the specific
style sheet language used by a STYLE element, must hide the contents of the
STYLE element. It is an error to render the content as part of the
document's text. Some style sheet languages support syntax for hiding the
content from non-conforming user agents.

The syntax of style data depends on the style sheet language.

Some style sheet implementations may allow a wider variety of rules in the
STYLE element than in the style attribute. For example, with CSS, rules may
be declared within a STYLE element for:

   * All instances of a specific HTML element (e.g., all P elements, all H1
     elements, etc.)
   * All instances of an HTML element belonging to a specific class (i.e.,
     whose class attribute is set to some value).
   * Single instances of an HTML element (i.e., whose id attribute is set to
     some value).

Rules for style rule precedences and inheritance depend on the style sheet
language.

The following CSS STYLE declaration puts a border around every H1 element in
the document and centers it on the page.

<HEAD>
 <STYLE type="text/css">
   H1 {border-width: 1; border: solid; text-align: center}
 </STYLE>
</HEAD>

To specify that this style information should only apply to H1 elements of a
specific class, we modify it as follows:

<HEAD>
 <STYLE type="text/css">
   H1.myclass {border-width: 1; border: solid; text-align: center}
 </STYLE>
</HEAD>
<BODY>
 <H1 class="myclass"> This H1 is affected by our style </H1>
 <H1> This one is not affected by our style </H1>
</BODY>

Finally, to limit the scope of the style information to a single instance of
H1, set the id attribute:

<HEAD>
 <STYLE type="text/css">
   #myid {border-width: 1; border: solid; text-align: center}
 </STYLE>
</HEAD>
<BODY>
 <H1 class="myclass"> This H1 is not affected </H1>
 <H1 id="myid"> This H1 is affected by style </H1>
 <H1> This H1 is not affected </H1>
</BODY>

Although style information may be set for almost every HTML element, two
elements, DIV and SPAN, are particularly useful in that they do not impose
any presentation semantics (besides block-level vs. inline). When combined
with style sheets, these elements allow users to extend HTML indefinitely,
particularly when used with the class and id attributes.

In the following example, we use the SPAN element to set the font style of
the first few words of a paragraph to small caps.

<HEAD>
 <STYLE type="text/css">
  SPAN.sc-ex { font-variant: small-caps }
 </STYLE>
</HEAD>
<BODY>
  <P><SPAN class="sc-ex">The first</SPAN> few words of
  this paragraph are in small-caps.
</BODY>

In the following example, we use DIV and the class attribute to set the text
justification for a series of paragraphs that make up the abstract section
of a scientific article. This style information could be reused for other
abstract sections by setting the class attribute elsewhere in the document.

<HEAD>
 <STYLE type="text/css">
   DIV.Abstract { text-align: justify }
 </STYLE>
</HEAD>
<BODY>
 <DIV class="Abstract">
   <P>The Chieftain product range is our market winner for
     the coming year. This report sets out how to position
     Chieftain against competing products.

   <P>Chieftain replaces the Commander range, which will
     remain on the price list until further notice.
 </DIV>
</BODY>

14.2.4 Media types

HTML allows authors to design documents that take advantage of the
characteristics of the media where the document is to be rendered (e.g.,
graphical displays, television screens, handheld devices, speech-based
browsers, braille-based tactile devices, etc.). By specifying the media
attribute, authors allow user agents to load and apply style sheets
selectively. Please consult the list of recognized media descriptors.

The following sample declarations apply to H1 elements. When projected in a
business meeting, all instances will be blue. When printed, all instances
will be centered.

<HEAD>
 <STYLE type="text/css" media="projection">
    H1 { color: blue}
 </STYLE>

 <STYLE type="text/css" media="print">
   H1 { text-align: center }
 </STYLE>

This example adds sound effects to anchors for use in speech output:

 <STYLE type="text/css" media="aural">
   A { cue-before: uri(bell.aiff); cue-after: uri(dong.wav)}
 </STYLE>
</HEAD>

Media control is particularly interesting when applied to external style
sheets since user agents can save time by retrieving from the network only
those style sheets that apply to the current device. For instance,
speech-based browsers can avoid downloading style sheets designed for visual
rendering. See the section on media-dependent cascades for more information.

14.3 External style sheets

Authors may separate style sheets from HTML documents. This offers several
benefits:

   * Authors and Web site managers may share style sheets across a number of
     documents (and sites).
   * Authors may change the style sheet without requiring modifications to
     the document.
   * User agents may load style sheets selectively (based on media
     descriptions).

14.3.1 Preferred and alternate style sheets

HTML allows authors to associate any number of external style sheets with a
document. The style sheet language defines how multiple external style
sheets interact (for example, the CSS "cascade" rules).

Authors may specify a number of mutually exclusive style sheets called
alternate style sheets. Users may select their favorite among these
depending on their preferences. For instance, an author may specify one
style sheet designed for small screens and another for users with weak
vision (e.g., large fonts). User agents should allow users to select from
alternate style sheets.

The author may specify that one of the alternates is a preferred style
sheet. User agents should apply the author's preferred style sheet unless
the user has selected a different alternate.

Authors may group several alternate style sheets (including the author's
preferred style sheets) under a single style name. When a user selects a
named style, the user agent must apply all style sheets with that name. User
agents must not apply alternate style sheets with a different style name.
The section on specifying external style sheets explains how to name a group
of style sheets.

Authors may also specify persistent style sheets that user agents must apply
in addition to any alternate style sheet.

User agents must respect media descriptors when applying any style sheet.

User agents should also allow users to disable the author's style sheets
entirely, in which case the user agent must not apply any persistent or
alternate style sheets.

14.3.2 Specifying external style sheets

Authors specify external style sheets with the following attributes of the
LINK element:

   * Set the value of href to the location of the style sheet file. The
     value of href is a URI.
   * Set the value of the type attribute to indicate the language of the
     linked (style sheet) resource. This allows the user agent to avoid
     downloading a style sheet for an unsupported style sheet language.
   * Specify that the style sheet is persistent, preferred, or alternate:
        o To make a style sheet persistent, set the rel attribute to
          "stylesheet" and don't set the title attribute.
        o To make a style sheet preferred, set the rel attribute to
          "stylesheet" and name the style sheet with the title attribute.
        o To specify an alternate style sheet, set the rel attribute to
          "alternate stylesheet" and name the style sheet with the title
          attribute.

User agents should provide a means for users to view and pick from the list
of alternate styles. The value of the title attribute is recommended as the
name of each choice.

In this example, we first specify a persistent style sheet located in the
file mystyle.css:

<LINK href="mystyle.css" rel="stylesheet" type="text/css">

Setting the title attribute makes this the author's preferred style sheet:

 <LINK href="mystyle.css" title="Compact" rel="stylesheet" type="text/css">

Adding the keyword "alternate" to the rel attribute makes it an alternate
style sheet:

<LINK href="mystyle.css" title="Medium" rel="alternate stylesheet" type="text/css">

For more information on external style sheets, please consult the section on
links and external style sheets.

Authors may also use the META element to set the document's preferred style
sheet. For example, to set the preferred style sheet to "compact" (see the
preceding example), authors may include the following line in the HEAD:

<META http-equiv="Default-Style" content="compact">

The preferred style sheet may also be specified with HTTP headers. The above
META declaration is equivalent to the HTTP header:

Default-Style: "compact"

If two or more META declarations or HTTP headers specify the preferred style
sheet, the last one takes precedence. HTTP headers are considered to occur
earlier than the document HEAD for this purpose.

If two or more LINK elements specify a preferred style sheet, the first one
takes precedence.

Preferred style sheets specified with META or HTTP headers have precedence
over those specified with the LINK element.

14.4 Cascading style sheets

Cascading style sheet languages such as CSS allow style information from
several sources to be blended together. However, not all style sheet
languages support cascading. To define a cascade, authors specify a sequence
of LINK and/or STYLE elements. The style information is cascaded in the
order the elements appear in the HEAD.

Note. This specification does not specify how style sheets from different
style languages cascade. Authors should avoid mixing style sheet languages.

In the following example, we specify two alternate style sheets named
"compact". If the user selects the "compact" style, the user agent must
apply both external style sheets, as well as the persistent "common.css"
style sheet. If the user selects the "big print" style, only the alternate
style sheet "bigprint.css" and the persistent "common.css" will be applied.

<LINK rel="alternate stylesheet" title="compact" href="small-base.css" type="text/css">
<LINK rel="alternate stylesheet" title="compact" href="small-extras.css" type="text/css">
<LINK rel="alternate stylesheet" title="big print" href="bigprint.css" type="text/css">
<LINK rel="stylesheet" href="common.css" type="text/css">

Here is a cascade example that involves both the LINK and STYLE elements.

<LINK rel="stylesheet" href="corporate.css" type="text/css">
<LINK rel="stylesheet" href="techreport.css" type="text/css">
<STYLE type="text/css">
    p.special { color: rgb(230, 100, 180) }
</STYLE>

14.4.1 Media-dependent cascades

A cascade may include style sheets applicable to different media. Both LINK
and STYLE may be used with the media attribute. The user agent is then
responsible for filtering out those style sheets that do not apply to the
current medium.

In the following example, we define a cascade where the "corporate" style
sheet is provided in several versions: one suited to printing, one for
screen use and one for speech-based browsers (useful, say, when reading
email in the car). The "techreport" stylesheet applies to all media. The
color rule defined by the STYLE element is used for print and screen but not
for aural rendering.

<LINK rel="stylesheet" media="aural" href="corporate-aural.css" type="text/css">
<LINK rel="stylesheet" media="screen" href="corporate-screen.css" type="text/css">
<LINK rel="stylesheet" media="print" href="corporate-print.css" type="text/css">
<LINK rel="stylesheet" href="techreport.css" type="text/css">
<STYLE type="text/css">
    p.special { color: rgb(230, 100, 180) }
</STYLE>

14.4.2 Inheritance and cascading

When the user agent wants to render a document, it needs to find values for
style properties, e.g. the font family, font style, size, line height, text
color and so on. The exact mechanism depends on the style sheet language,
but the following description is generally applicable:

The cascading mechanism is used when a number of style rules all apply
directly to an element. The mechanism allows the user agent to sort the
rules by specificity, to determine which rule to apply. If no rule can be
found, the next step depends on whether the style property can be inherited
or not. Not all properties can be inherited. For these properties the style
sheet language provides default values for use when there are no explicit
rules for a particular element.

If the property can be inherited, the user agent examines the immediately
enclosing element to see if a rule applies to that. This process continues
until an applicable rule is found. This mechanism allows style sheets to be
specified compactly. For instance, authors may specify the font family for
all elements within the BODY by a single rule that applies to the BODY
element.

14.5 Hiding style data from user agents

Some style sheet languages support syntax intended to allow authors to hide
the content of STYLE elements from non-conforming user agents.

This example illustrates for CSS how to comment out the content of STYLE
elements to ensure that older non-conforming user agents will not render
them as text.

<STYLE type="text/css">
<!--
   H1 { color: red }
   P  { color: blue}
   -->
</STYLE>

14.6 Linking to style sheets with HTTP headers

Web server managers may find it convenient to configure a server so that a
style sheet will be applied to a group of pages. The HTTP Link header
described in [RFC2068], section 19.6.1.2, has the same effect as a LINK
element with the same attributes and values. Multiple Link headers
correspond to multiple LINK elements occurring in the same order. For
instance,

Link: <http://www.acme.com/corporate.css>; REL=stylesheet

corresponds to:

<LINK rel="stylesheet" href="http://www.acme.com/corporate.css">

It is possible to specify several alternate styles using multiple Link
headers, and then use the rel attribute to determine the default style.

In the following example, "compact" is applied by default since it omits the
"alternate" keyword for the rel attribute.

Link: <compact.css>; rel="stylesheet"; title="compact"
Link: <bigprint.css>; rel="alternate stylesheet"; title="big print"

This should also work when HTML documents are sent by email. Some email
agents can alter the ordering of [RFC822] headers. To protect against this
affecting the cascading order for style sheets specified by Link headers,
authors can use header concatenation to merge several instances of the same
header field. The quote marks are only needed when the attribute values
include whitespace. Use SGML entities to reference characters that are
otherwise not permitted within HTTP or email headers, or that are likely to
be affected by transit through gateways.

LINK and META elements implied by HTTP headers are defined as occurring
before any explicit LINK and META elements in the document's HEAD.

               15 Alignment, font styles, and horizontal rules

Contents

  1. Formatting
       1. Background color
       2. Alignment
       3. Floating objects
             + Float an object
             + Float text around an object
  2. Fonts
       1. Font style elements: the TT, I, B, BIG, SMALL, STRIKE, S, and U
          elements
       2. Font modifier elements: FONT and BASEFONT
  3. Rules: the HR element

This section of the specification discusses some HTML elements and
attributes that may be used for visual formatting of elements. Many of them
are deprecated.

15.1 Formatting

15.1.1 Background color

Attribute definitions

bgcolor = color [CI]
     Deprecated. This attribute sets the background color for the document
     body or table cells.

This attribute sets the background color of the canvas for the document body
(the BODY element) or for tables (the TABLE, TR, TH, and TD elements).
Additional attributes for specifying text color can be used with the BODY
element.

This attribute has been deprecated in favor of style sheets for specifying
background color information.

15.1.2 Alignment

It is possible to align block elements (tables, images, objects, paragraphs,
etc.) on the canvas with the align element. Although this attribute may be
set for many HTML elements, its range of possible values sometimes differs
from element to element. Here we only discuss the meaning of the align
attribute for text.

Attribute definitions

align = left|center|right|justify [CI]
     Deprecated. This attribute specifies the horizontal alignment of its
     element with respect to the surrounding context. Possible values:
        o left: text lines are rendered flush left.
        o center: text lines are centered.
        o right: text lines are rendered flush right.
        o justify: text lines are justified to both margins.

The default depends on the base text direction. For left to right text, the
default is align=left, while for right to left text, the default is
align=right.

DEPRECATED EXAMPLE:
This example centers a heading on the canvas.

<H1 align="center"> How to Carve Wood </H1>

Using CSS, for example, you could achieve the same effect as follows:

<HEAD>
 <TITLE>How to Carve Wood</TITLE>
 <STYLE type="text/css">
  H1 { text-align: center}
 </STYLE>
<BODY>
 <H1> How to Carve Wood </H1>

Note that this would center all H1 declarations. You could reduce the scope
of the style by setting the class attribute on the element:

<HEAD>
 <TITLE>How to Carve Wood</TITLE>
 <STYLE type="text/css">
  H1.wood {text-align: center}
 </STYLE>
<BODY>
 <H1 class="wood"> How to Carve Wood </H1>

DEPRECATED EXAMPLE:
Similarly, to right align a paragraph on the canvas with HTML's align
attribute you could have:

<P align="right">...Lots of paragraph text...

which, with CSS, would be:

<HEAD>
 <TITLE>How to Carve Wood</TITLE>
 <STYLE type="text/css">
  P.mypar {text-align: right}
 </STYLE>
<BODY>
 <P class="mypar">...Lots of paragraph text...

DEPRECATED EXAMPLE:
To right align a series of paragraphs, group them with the DIV element:

<DIV align="right">
 <P>...text in first paragraph...
 <P>...text in second paragraph...
 <P>...text in third paragraph...
</DIV>

With CSS, the text-align property is inherited from the parent element, you
can therefore use:

<HEAD>
 <TITLE>How to Carve Wood</TITLE>
 <STYLE type="text/css">
  DIV.mypars {text-align: right}
 </STYLE>
<BODY>
 <DIV class="mypars">
  <P>...text in first paragraph...
  <P>...text in second paragraph...
  <P>...text in third paragraph...
 </DIV>

To center the entire document with CSS:

<HEAD>
 <TITLE>How to Carve Wood</TITLE>
 <STYLE type="text/css">
  BODY {text-align: center}
 </STYLE>
<BODY>
 ...the body is centered...
</BODY>

The CENTER element is exactly equivalent to specifying the DIV element with
the align attribute set to "center". The CENTER element is deprecated.

15.1.3 Floating objects

Images and objects may appear directly "in-line" or may be floated to one
side of the page, temporarily altering the margins of text that may flow on
either side of the object.

Float an object

The align attribute for object, images, tables, frames, etc., causes the
object to float to the left or right margin. Floating objects generally
begin a new line. This attribute takes the following values:

   * left: Floats the object to the current left margin. Subsequent text
     flows along the image's right side.
   * right: Floats the object to the current right margin. Subsequent text
     flows along the image's left side.

DEPRECATED EXAMPLE:
The following example shows how to float an IMG element to the current left
margin of the canvas.

<IMG align="left" src="http://foo.com/animage.gif" alt="my boat">

Some alignment attributes also permit the "center" value, which does not
cause floating, but centers the object within the current margins. However,
for P and DIV, the value "center" causes the contents of the element to be
centered.

Float text around an object

Another attribute, defined for the BR element, controls text flow around
floating objects.

Attribute definitions

clear = none|left|right|all [CI]
     Deprecated. Specifies where the next line should appear in a visual
     browser after the line break caused by this element. This attribute
     takes into account floating objects (images, tables, etc.). Possible
     values:
        o none: The next line will begin normally. This is the default
          value.
        o left: The next line will begin at nearest line below any floating
          objects on the left-hand margin.
        o right: The next line will begin at nearest line below any floating
          objects on the right-hand margin.
        o all: The next line will begin at nearest line below any floating
          objects on either margin.

Consider the following visual scenario, where text flows to the right of an
image until a line is broken by a BR:

*********  -------
|       |  -------
| image |  --<BR>
|       |
*********

If the clear attribute is set to none, the line following BR will begin
immediately below it at the right margin of the image:

*********  -------
|       |  -------
| image |  --<BR>
|       |  ------
*********

DEPRECATED EXAMPLE:
If the clear attribute is set to left or all, next line will appear as
follows:

*********  -------
|       |  -------
| image |  --<BR clear="left">
|       |
*********
-----------------

Using style sheets, you could specify that all line breaks should behave
this way for objects (images, tables, etc.) floating against the left
margin. With CSS, you could achieve this as follows:

<STYLE type="text/css">
BR { clear: left }
</STYLE>

To specify this behavior for a specific instance of the BR element, you
could combine style information and the id attribute:

<HEAD>
...
<STYLE type="text/css">
BR.mybr { clear: left }
</STYLE>
</HEAD>
<BODY>
<P>...
*********  -------
|       |  -------
| table |  --<BR id="mybr">
|       |
*********
-----------------
...
</BODY>

15.2 Fonts

The following HTML elements specify font information. Although they are not
all deprecated, their use is discouraged in favor of style sheets.

15.2.1 Font style elements: the TT, I, B, BIG, SMALL, STRIKE, S, and U
elements

<!ENTITY % fontstyle
 "TT | I | B | BIG | SMALL">
<!ELEMENT (%fontstyle;|%phrase;) - - (%inline;)*>
<!ATTLIST (%fontstyle;|%phrase;)
  %attrs;                              -- %coreattrs, %i18n, %events --
  >

Start tag: required, End tag: required

Attributes defined elsewhere

   * id, class (document-wide identifiers)
   * lang (language information), dir (text direction)
   * title (element title)
   * style (inline style information)
   * onclick, ondblclick, onmousedown, onmouseup, onmouseover, onmousemove,
     onmouseout, onkeypress, onkeydown onkeyup (intrinsic events)

Rendering of font style elements depends on the user agent. The following is
an informative description only.

     TT: Renders as teletype or monospaced text.
     I: Renders as italic text style.
     B: Renders as bold text style.
     BIG: Renders text in a "large" font.
     SMALL: Renders text in a "small" font.
     STRIKE and S: Deprecated. Render strike-through style text.
     U: Deprecated. Renders underlined text.

The following sentence shows several types of text:

<P><b>bold</b>,
<i>italic</i>, <b><i>bold italic</i></b>, <tt>teletype text</tt>, and
<big>big</big> and <small>small</small> text.

These words might be rendered as follows:

[An example of rendering of various font styles]

It is possible to achieve a much richer variety of font effects using style
sheets. To specify blue, italic text in a paragraph with CSS:

<HEAD>
<STYLE type="text/css">
P.mypar {font-style: italic; color: blue}
</STYLE>
</HEAD>
<P id="mypar">...Lots of blue italic text...

Font style elements must be properly nested. Rendering of nested font style
elements depends on the user agent.

15.2.2 Font modifier elements: FONT and BASEFONT

FONT and BASEFONT are deprecated.

See the Transitional DTD for the formal definition.

Attribute definitions

size  = cdata [CN]
     Deprecated. This attribute sets the size of the font. Possible values:
        o An integer between 1 and 7. This sets the font to some fixed size,
          whose rendering depends on the user agent. Not all user agents may
          render all seven sizes.
        o A relative increase in font size. The value "+1" means one size
          larger. The value "-3" means three sizes smaller. All sizes belong
          to the scale of 1 to 7.
color = color [CI]
     Deprecated. This attribute sets the text color.
face = cdata [CI]
     Deprecated. This attribute defines a comma-separated list of font names
     the user agent should search for in order of preference.

Attributes defined elsewhere

   * id, class (document-wide identifiers)
   * lang (language information), dir (text direction)
   * title (element title)
   * style (inline style information)

The FONT element changes the font size and color for text in its contents.

The BASEFONT element sets the base font size (using the size attribute).
Font size changes achieved with FONT are relative to the base font size set
by BASEFONT. If BASEFONT is not used, the default base font size is 3.

DEPRECATED EXAMPLE:
The following example will show the difference between the seven font sizes
available with FONT:

<P><font size=1>size=1</font>
<font size=2>size=2</font>
<font size=3>size=3</font>
<font size=4>size=4</font>
<font size=5>size=5</font>
<font size=6>size=6</font>
<font size=7>size=7</font>

This might be rendered as:

[Example of rendering of various font sizes]

The following shows an example of the effect of relative font sizes using a
base font size of 3:

[Example of rendering of various font sizes with a basefont]

The base font size does not apply to headings, except where these are
modified using the FONT element with a relative font size change.

15.3 Rules: the HR element

<!ELEMENT HR - O EMPTY -- horizontal rule -->
<!ATTLIST HR
  %coreattrs;                          -- id, class, style, title --
  %events;
  >

Start tag: required, End tag: forbidden

Attribute definitions

align = left|center|right [CI]
     Deprecated. This attribute specifies the horizontal alignment of the
     rule with respect to the surrounding context. Possible values:
        o left: the rule is rendered flush left.
        o center: the rule is centered.
        o right: the rule is rendered flush right.

     The default is align=center.
noshade [CI]
     Deprecated. When set, this boolean attribute requests that the user
     agent render the rule in a solid color rather than as the traditional
     two-color "groove".
size = pixels [CI]
     Deprecated. This attribute specifies the height of the rule. The
     default value for this attribute depends on the user agent.
width = length [CI]
     Deprecated. This attribute specifies the width of the rule. The default
     width is 100%, i.e., the rule extends across the entire canvas.

Attributes defined elsewhere

   * id, class (document-wide identifiers)
   * lang (language information), dir (text direction)
   * title (element title)
   * style (inline style information)
   * onclick, ondblclick, onmousedown, onmouseup, onmouseover, onmousemove,
     onmouseout, onkeypress, onkeydown, onkeyup (intrinsic events)
   * align (alignment)

The HR element causes a horizontal rule to be rendered by visual user
agents.

The amount of vertical space inserted between a rule and the content that
surrounds it depends on the user agent.

DEPRECATED EXAMPLE:
This example centers the rules, sizing them to half the available width
between the margins. The top rule has the default thickness while the bottom
two are set to 5 pixels. The bottom rule should be rendered in a solid color
without shading:

<HR width="50%" align="center">
<HR size="5" width="50%" align="center">
<HR noshade size="5" width="50%" align="center">

These rules might be rendered as follows:

             [Example of rendering of various horizontal rules]

                                  16 Frames

Contents

  1. Introduction to frames
  2. Layout of frames
       1. The FRAMESET element
             + Rows and columns
             + Nested frame sets
             + Sharing data among frames
       2. The FRAME element
             + Setting the initial contents of a frame
             + Visual rendering of a frame
  3. Specifying target frame information
       1. Setting the default target for links
       2. Target semantics
  4. Alternate content
       1. The NOFRAMES element
       2. Long descriptions of frames
  5. Inline frames: the IFRAME element

16.1 Introduction to frames

HTML frames allow authors to present documents in multiple views, which may
be independent windows or subwindows. Multiple views offer designers a way
to keep certain information visible, while other views are scrolled or
replaced. For example, within the same window, one frame might display a
static banner, a second a navigation menu, and a third the main document
that can be scrolled though or replaced by navigating in the second frame.

Here is a simple frame document:

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Frameset//EN"
   "_THE_LATEST_VERSION_/frameset.dtd">
<HTML>
<HEAD>
<TITLE>A simple frameset document</TITLE>
</HEAD>
<FRAMESET cols="20%, 80%">
  <FRAMESET rows="100, 200">
      <FRAME src="contents_of_frame1.html">
      <FRAME src="contents_of_frame2.gif">
  </FRAMESET>
  <FRAME src="contents_of_frame3.html">
  <NOFRAMES>
      <P>This frameset document contains:
      <UL>
         <LI><A href="contents_of_frame1.html">Some neat contents</A>
         <LI><IMG src="contents_of_frame2.gif" alt="A neat image">
         <LI><A href="contents_of_frame3.html">Some other neat contents</A>
      </UL>
  </NOFRAMES>
</FRAMESET>
</HTML>

that might create a frame layout something like this:

 ---------------------------------------
|         |                             |
|         |                             |
| Frame 1 |                             |
|         |                             |
|         |                             |
|---------|                             |
|         |          Frame 3            |
|         |                             |
|         |                             |
|         |                             |
| Frame 2 |                             |
|         |                             |
|         |                             |
|         |                             |
|         |                             |
 ---------------------------------------

If the user agent can't display frames or is configured not to, it will
render the contents of the NOFRAMES element.

16.2 Layout of frames

An HTML document that describes frame layout (called a frameset document)
has a different makeup than an HTML document without frames. A standard
document has one HEAD section and one BODY. A frameset document has a HEAD,
and a FRAMESET in place of the BODY.

The FRAMESET section of a document specifies the layout of views in the main
user agent window. In addition, the FRAMESET section can contain a NOFRAMES
element to provide alternate content for user agents that do not support
frames or are configured not to display frames.

Elements that might normally be placed in the BODY element must not appear
before the first FRAMESET element or the FRAMESET will be ignored.

16.2.1 The FRAMESET element

<![ %HTML.Frameset; [
<!ELEMENT FRAMESET - - ((FRAMESET|FRAME)+ & NOFRAMES?) -- window subdivision-->
<!ATTLIST FRAMESET
  %coreattrs;                          -- id, class, style, title --
  rows        %MultiLengths; #IMPLIED  -- list of lengths,
                                          default: 100% (1 row) --
  cols        %MultiLengths; #IMPLIED  -- list of lengths,
                                          default: 100% (1 col) --
  onload      %Script;       #IMPLIED  -- all the frames have been loaded  --
  onunload    %Script;       #IMPLIED  -- all the frames have been removed --
  >
]]>

Attribute definitions

rows = multi-length-list [CN]
     This attribute specifies the layout of horizontal frames. It is a
     comma-separated list of pixels, percentages, and relative lengths. The
     default value is 100%, meaning one row.
cols = = multi-length-list [CN]
     This attribute specifies the layout of vertical frames. It is a
     comma-separated list of pixels, percentages, and relative lengths. The
     default value is 100%, meaning one column.

Attributes defined elsewhere

   * id, class (document-wide identifiers)
   * title (element title)
   * style (inline style information)
   * onload, onunload (intrinsic events)

The FRAMESET element specifies the layout of the main user window in terms
of rectangular subspaces.

Rows and columns

Setting the rows attribute defines the number of horizontal subspaces in a
frameset. Setting the cols attribute defines the number of vertical
subspaces. Both attributes may be set simultaneously to create a grid.

If the rows attribute is not set, each column extends the entire length of
the page. If the cols attribute is not set, each row extends the entire
width of the page. If neither attribute is set, the frame takes up exactly
the size of the page.

Frames are created left-to-right for columns and top-to-bottom for rows.
When both attributes are specified, views are created left-to-right in the
top row, left-to-right in the second row, etc.

The first example divides the screen vertically in two (i.e., creates a top
half and a bottom half).

<FRAMESET rows="50%, 50%">
...the rest of the definition...
</FRAMESET>

The next example creates three columns: the second has a fixed width of 250
pixels (useful, for example, to hold an image with a known size). The first
receives 25% of the remaining space and the third 75% of the remaining
space.

<FRAMESET cols="1*,250,3*">
...the rest of the definition...
</FRAMESET>

The next example creates a 2x3 grid of subspaces.

<FRAMESET rows="30%,70%" cols="33%,34%,33%">
...the rest of the definition...
</FRAMESET>

For the next example, suppose the browser window is currently 1000 pixels
high. The first view is allotted 30% of the total height (300 pixels). The
second view is specified to be exactly 400 pixels high. This leaves 300
pixels to be divided between the other two frames. The fourth frame's height
is specified as "2*", so it is twice as high as the third frame, whose
height is only "*" (equivalent to 1*). Therefore the third frame will be 100
pixels high and the fourth will be 200 pixels high.

<FRAMESET rows="30%,400,*,2*">
...the rest of the definition...
</FRAMESET>

Absolute lengths that do not sum to 100% of the real available space should
be adjusted by the user agent. When underspecified, remaining space should
be allotted proportionally to each view. When overspecified, each view
should be reduced according to its specified proportion of the total space.

Nested frame sets

Framesets may be nested to any level.

In the following example, the outer FRAMESET divides the available space
into three equal columns. The inner FRAMESET then divides the second area
into two rows of unequal height.

<FRAMESET cols="33%, 33%, 34%">
     ...contents of first frame...
     <FRAMESET rows="40%, 50%">
        ...contents of second frame, first row...
        ...contents of second frame, second row...
     </FRAMESET>
     ...contents of third frame...
</FRAMESET>

Sharing data among frames

Authors may share data among several frames by including this data via an
OBJECT element. Authors should include the OBJECT element in the HEAD
element of a frameset document and name it with the id attribute. Any
document that is the contents of a frame in the frameset may refer to this
identifier.

The following example illustrates how a script might refer to an OBJECT
element defined for an entire frameset:

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Frameset//EN"
   "_THE_LATEST_VERSION_/frameset.dtd">
<HTML>
<HEAD>
<TITLE>This is a frameset with OBJECT in the HEAD</TITLE>
<!-- This OBJECT is not rendered! -->
<OBJECT id="myobject" data="data.bar"></OBJECT>
</HEAD>
<FRAMESET>
    <FRAME src="bianca.html" name="bianca">
</FRAMESET>
</HTML>

<!-- In bianca.html -->
<HTML>
<HEAD>
<TITLE>Bianca's page</TITLE>
</HEAD>
<BODY>
...the beginning of the document...
<P>
<SCRIPT type="text/javascript">
parent.myobject.myproperty
</SCRIPT>
...the rest of the document...
</BODY>
</HTML>

16.2.2 The FRAME element

<![ %HTML.Frameset; [
<!-- reserved frame names start with "_" otherwise starts with letter -->
<!ELEMENT FRAME - O EMPTY              -- subwindow -->
<!ATTLIST FRAME
  %coreattrs;                          -- id, class, style, title --
  longdesc    %URI;          #IMPLIED  -- link to long description
                                          (complements title) --
  name        CDATA          #IMPLIED  -- name of frame for targetting --
  src         %URI;          #IMPLIED  -- source of frame content --
  frameborder (1|0)          1         -- request frame borders? --
  marginwidth %Pixels;       #IMPLIED  -- margin widths in pixels --
  marginheight %Pixels;      #IMPLIED  -- margin height in pixels --
  noresize    (noresize)     #IMPLIED  -- allow users to resize frames? --
  scrolling   (yes|no|auto)  auto      -- scrollbar or none --
  >
]]>

Attribute definitions

name = cdata [CI]
     This attribute assigns a name to the current frame. This name may be
     used as the target of subsequent links.
longdesc = uri [CT]
     This attribute specifies a link to a long description of the frame.
     This description should supplement the short description provided using
     the title attribute, and may be particularly useful for non-visual user
     agents.
src = uri [CT]
     This attribute specifies the location of the initial contents to be
     contained in the frame.
noresize [CI]
     When present, this boolean attribute tells the user agent that the
     frame window must not be resizeable.
scrolling = auto|yes|no [CI]
     This attribute specifies scroll information for the frame window.
     Possible values
        o auto: This value tells the user agent to provide scrolling devices
          for the frame window when necessary. This is the default value.
        o yes: This value tells the user agent to always provide scrolling
          devices for the frame window.
        o no: This value tells the user agent not to provide scrolling
          devices for the frame window.
frameborder = 1|0 [CN]
     This attribute provides the user agent with information about the frame
     border. Possible values:
        o 1: This value tells the user agent to draw a separator between
          this frame and every adjoining frame. This is the default value.
        o 0: This value tells the user agent not to draw a separator between
          this frame and every adjoining frame. Note that separators may be
          drawn next to this frame nonetheless if specified by other frames.
marginwidth = pixels [CN]
     This attribute specifies the amount of space to be left between the
     frame's contents in its left and right margins. The value must be
     greater than one pixel. The default value depends on the user agent.
marginheight = pixels [CN]
     This attribute specifies the amount of space to be left between the
     frame's contents in its top and bottom margins. The value must be
     greater than one pixel. The default value depends on the user agent.

Attributes defined elsewhere

   * id, class (document-wide identifiers)
   * title (element title)
   * style (inline style information)
   * target (target frame information)

The FRAME element defines the contents and appearance of a single frame.

Setting the initial contents of a frame

The src attribute specifies the initial document the frame will contain.

The following example HTML document:

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Frameset//EN"
   "_THE_LATEST_VERSION_/frameset.dtd">
<HTML>
<HEAD>
<TITLE>A frameset document</TITLE>
</HEAD>
<FRAMESET cols="33%,33%,33%">
  <FRAMESET rows="*,200">
      <FRAME src="contents_of_frame1.html">
      <FRAME src="contents_of_frame2.gif">
  </FRAMESET>
  <FRAME src="contents_of_frame3.html">
  <FRAME src="contents_of_frame4.html">
</FRAMESET>
</HTML>

should create a frame layout something like this:

 ------------------------------------------
|Frame 1     |Frame 3       |Frame 4       |
|            |              |              |
|            |              |              |
|            |              |              |
|            |              |              |
|            |              |              |
|            |              |              |
|            |              |              |
-------------|              |              |
|Frame 2     |              |              |
|            |              |              |
|            |              |              |
 ------------------------------------------

and cause the user agent to load each file into a separate view.

The contents of a frame must not be in the same document as the frame's
definition.

ILLEGAL EXAMPLE:
The following frameset definition is not legal HTML since the contents of
the second frame are in the same document as the frameset.

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Frameset//EN"
   "_THE_LATEST_VERSION_/frameset.dtd">
<HTML>
<HEAD>
<TITLE>A frameset document</TITLE>
</HEAD>
<FRAMESET cols="50%,50%">
  <FRAME src="contents_of_frame1.html">
  <FRAME src="#anchor_in_same_document">
  <NOFRAMES>
  ...some text...
  <H2><A name="anchor_in_same_document">Important section</A></H2>
  ...some text...
  </NOFRAMES>
</FRAMESET>
</HTML>

Visual rendering of a frame

The following example illustrates the usage of the decorative FRAME
attributes. We specify that frame 1 will allow no scroll bars. Frame 2 will
leave white space around its contents (initially, an image file) and the
frame will not be resizeable. No border will be drawn between frames 3 and
4. Borders will be drawn (by default) between frames 1, 2, and 3.

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Frameset//EN"
   "_THE_LATEST_VERSION_/frameset.dtd">
<HTML>
<HEAD>
<TITLE>A frameset document</TITLE>
</HEAD>
<FRAMESET cols="33%,33%,33%">
  <FRAMESET rows="*,200">
      <FRAME src="contents_of_frame1.html" scrolling="no">
      <FRAME src="contents_of_frame2.gif"
                marginwidth="10" marginheight="15"
                noresize>
  </FRAMESET>
  <FRAME src="contents_of_frame3.html" frameborder="0">
  <FRAME src="contents_of_frame4.html" frameborder="0">
</FRAMESET>
</HTML>

16.3 Specifying target frame information

Note. For information about current practice in determining the target of a
frame, please consult the notes on frames in the appendix.

Attribute definitions

target = frame-target [CI]
     This attribute specifies the name of a frame where a document is to be
     opened.

By assigning a name to a frame via the name attribute, authors can refer to
it as the "target" of links defined by other elements. The target attribute
may be set for elements that create links (A, LINK), image maps (AREA), and
forms (FORM).

Please consult the section on target frame names for information about
recognized frame names.

This example illustrates how targets allow the dynamic modification of a
frame's contents. First we define a frameset in the document frameset.html,
shown here:

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Frameset//EN"
   "_THE_LATEST_VERSION_/frameset.dtd">
<HTML>
<HEAD>
<TITLE>A frameset document</TITLE>
</HEAD>
<FRAMESET rows="50%,50%">
   <FRAME name="fixed" src="init_fixed.html">
   <FRAME name="dynamic" src="init_dynamic.html">
</FRAMESET>
</HTML>

Then, in init_dynamic.html, we link to the frame named "dynamic".

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Frameset//EN"
   "_THE_LATEST_VERSION_/frameset.dtd">
<HTML>
<HEAD>
<TITLE>A document with anchors with specific targets</TITLE>
</HEAD>
<BODY>
...beginning of the document...
<P>Now you may advance to
    <A href="slide2.html" target="dynamic">slide 2.</A>
...more document...
<P>You're doing great. Now on to
    <A href="slide3.html" target="dynamic">slide 3.</A>
</BODY>
</HTML>

Activating either link opens a new document in the frame named "dynamic"
while the other frame, "fixed", maintains its initial contents.

Note. A frameset definition never changes, but the contents of one of its
frames can. Once the initial contents of a frame change, the frameset
definition no longer reflects the current state of its frames.

There is currently no way to encode the entire state of a frameset in a URI.
Therefore, many user agents do not allow users to assign a bookmark to a
frameset.

Framesets may make navigation forward and backward through your user agent's
history more difficult for users.

16.3.1 Setting the default target for links

When many links in the same document designate the same target, it is
possible to specify the target once and dispense with the target attribute
of each element. This is done by setting the target attribute of the BASE
element.

We return to the previous example, this time factorizing the target
information by defining it in the BASE element and removing it from the A
elements.

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Frameset//EN"
   "_THE_LATEST_VERSION_/frameset.dtd">
<HTML>
<HEAD>
<TITLE>A document with BASE with a specific target</TITLE>
<BASE href="http://www.mycom.com/Slides" target="dynamic">
</HEAD>
<BODY>
...beginning of the document...
<P>Now you may advance to <A href="slide2.html">slide 2.</A>
...more document...
<P>You're doing great. Now on to
       <A href="slide3.html">slide 3.</A>
</BODY>
</HTML>

16.3.2 Target semantics

User agents should determine the target frame in which to load a linked
resource according to the following precedences (highest priority to
lowest):

  1. If an element has its target attribute set to a known frame, when the
     element is activated (i.e., a link is followed or a form is processed),
     the resource designated by the element should be loaded into the target
     frame.
  2. If an element does not have the target attribute set but the BASE
     element does, the BASE element's target attribute determines the frame.
  3. If neither the element nor the BASE element refers to a target, the
     resource designated by the element should be loaded into the frame
     containing the element.
  4. If any target attribute refers to an unknown frame F, the user agent
     should create a new window and frame, assign the name F to the frame,
     and load the resource designated by the element in the new frame.

User agents may provide users with a mechanism to override the target
attribute.

16.4 Alternate content

Authors should supply alternate content for those user agents that do not
support frames or are configured not to display frames.

16.4.1 The NOFRAMES element

<![ %HTML.Frameset; [
<!ENTITY % noframes.content "(BODY) -(NOFRAMES)">
]]>

<!ENTITY % noframes.content "(%flow;)*">

<!ELEMENT NOFRAMES - - %noframes.content;
 -- alternate content container for non frame-based rendering -->
<!ATTLIST NOFRAMES
  %attrs;                              -- %coreattrs, %i18n, %events --
  >

The NOFRAMES element specifies content that should be displayed only when
frames are not being displayed. User agents that support frames must only
display the contents of a NOFRAMES declaration when configured not to
display frames. User agents that do not support frames must display the
contents of NOFRAMES in any case.

NOFRAMES can be used in the FRAMESET section of a frameset document.

For example:

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Frameset//EN"
     "_THE_LATEST_VERSION_">
  <HTML>
  <HEAD>
  <TITLE>A frameset document with NOFRAMES</TITLE>
  </HEAD>
  <FRAMESET cols="50%, 50%">
     <FRAME src="main.html">
     <FRAME src="table_of_contents.html">
     <NOFRAMES>
     <P>Here is the <A href="main-noframes.html">
              non-frame based version of the document.</A>
     </NOFRAMES>
  </FRAMESET>
  </HTML>

16.4.2 Long descriptions of frames

The longdesc attribute allows authors to make frame documents more
accessible to people using non-visual user agents. This attribute designates
a resource that provides a long description of the frame. Authors should
note that long descriptions associated with frames are attached to the
frame, not the frame's contents. Since the contents may vary over time, the
initial long description is likely to become inappropriate for the frame's
later contents. In particular, authors should not include an image as the
sole content of a frame.

The following frameset document describes two frames. The left frame
contains a table of contents and the right frame initially contains an image
of an ostrich:

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Frameset//EN"
   "_THE_LATEST_VERSION_">
<HTML>
<HEAD>
<TITLE>A poorly-designed frameset document</TITLE>
</HEAD>
<FRAMESET cols="20%, 80%">
   <FRAME src="table_of_contents.html">
   <FRAME src="ostrich.gif" longdesc="ostrich-desc.html">
</FRAMESET>
</HTML>

Note that the image has been included in the frame independently of any HTML
element, so the author has no means of specifying alternate text other than
via the longdesc attribute. If the contents of the right frame change (e.g.,
the user selects a rattlesnake from the table of contents), users will have
no textual access to the frame's new content.

Thus, authors should not put an image directly in a frame. Instead, the
image should be specified in a separate HTML document, and therein annotated
with the appropriate alternate text:

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Frameset//EN"
   "_THE_LATEST_VERSION_">
<HTML>
<HEAD>
<TITLE>A well-designed frameset document</TITLE>
</HEAD>
<FRAMESET cols="20%, 80%">
   <FRAME src="table_of_contents.html">
   <FRAME src="ostrich-container.html">
</FRAMESET>
</HTML>

<!-- In ostrich-container.html: -->
<HTML>
<HEAD>
<TITLE>The fast and powerful ostrich</TITLE>
</HEAD>
<P>
<OBJECT data="ostrich.gif" type="image/gif">
These ostriches sure taste good!
</OBJECT>
</HTML>

16.5 Inline frames: the IFRAME element

<!ELEMENT IFRAME - - (%flow;)*         -- inline subwindow -->
<!ATTLIST IFRAME
  %coreattrs;                          -- id, class, style, title --
  longdesc    %URI;          #IMPLIED  -- link to long description
                                          (complements title) --
  name        CDATA          #IMPLIED  -- name of frame for targetting --
  src         %URI;          #IMPLIED  -- source of frame content --
  frameborder (1|0)          1         -- request frame borders? --
  marginwidth %Pixels;       #IMPLIED  -- margin widths in pixels --
  marginheight %Pixels;      #IMPLIED  -- margin height in pixels --
  scrolling   (yes|no|auto)  auto      -- scrollbar or none --
  align       %IAlign;       #IMPLIED  -- vertical or horizontal alignment --
  height      %Length;       #IMPLIED  -- frame height --
  width       %Length;       #IMPLIED  -- frame width --
  >

Attribute definitions

longdesc = uri [CT]
     This attribute specifies a link to a long description of the frame.
     This description should supplement the short description provided using
     the title attribute, and is particularly useful for non-visual user
     agents.
name = cdata [CI]
     This attribute assigns a name to the current frame. This name may be
     used as the target of subsequent links.
width = length [CN]
     The width of the inline frame.
height = length [CN]
     The height of the inline frame.

Attributes defined elsewhere

   * id, class (document-wide identifiers)
   * title (element title)
   * style (inline style information)
   * name, src, frameborder, marginwidth, marginheight, scrolling (frame
     controls and decoration)
   * target (target frame information)
   * align (alignment)

The IFRAME element allows authors to insert a frame within a block of text.
Inserting an inline frame within a section of text is much like inserting an
object via the OBJECT element: they both allow you to insert an HTML
document in the middle of another, they may both be aligned with surrounding
text, etc.

The information to be inserted inline is designated by the src attribute of
this element. The contents of the IFRAME element, on the other hand, should
only be displayed by user agents that do not support frames or are
configured not to display frames.

For user agents that support frames, the following example will place an
inline frame surrounded by a border in the middle of the text.

  <IFRAME src="foo.html" width="400" height="500"
             scrolling="auto" frameborder="1">
  [Your user agent does not support frames or is currently configured
  not to display frames. However, you may visit
  <A href="foo.html">the related document.</A>]
  </IFRAME>

Inline frames may not be resized (and thus, they do not take the noresize
attribute).

Note. HTML documents may also be embedded in other HTML documents with the
OBJECT element. See the section on embedded documents for details.

                                  17 Forms

Contents

  1. Introduction to forms
  2. Controls
       1. Control types
  3. The FORM element
  4. The INPUT element
       1. Control types created with INPUT
       2. Examples of forms containing INPUT controls
  5. The BUTTON element
  6. The SELECT, OPTGROUP, and OPTION elements
       1. Preselected options
  7. The TEXTAREA element
  8. The ISINDEX element
  9. Labels
       1. The LABEL element
 10. Adding structure to forms: the FIELDSET and LEGEND elements
 11. Giving focus to an element
       1. Tabbing navigation
       2. Access keys
 12. Disabled and read-only controls
       1. Disabled controls
       2. Read-only controls
 13. Form submission
       1. Form submission method
       2. Successful controls
       3. Processing form data
             + Step one: Identify the successful controls
             + Step two: Build a form data set
             + Step three: Encode the form data set
             + Step four: Submit the encoded form data set
       4. Form content types
             + application/x-www-form-urlencoded
             + multipart/form-data

17.1 Introduction to forms

An HTML form is a section of a document containing normal content, markup,
special elements called controls (checkboxes, radio buttons, menus, etc.),
and labels on those controls. Users generally "complete" a form by modifying
its controls (entering text selecting menu items, etc.), before submitting
the form to an agent for processing (e.g., to a Web server, to a mail
server, etc.)

Here's a simple form that includes labels, radio buttons, and push buttons
(reset the form or submit it):

 <FORM action="http://somesite.com/prog/adduser" method="post">
    <P>
    <LABEL for="firstname">First name: </LABEL>
              <INPUT type="text" id="firstname"><BR>
    <LABEL for="lastname">Last name: </LABEL>
              <INPUT type="text" id="lastname"><BR>
    <LABEL for="email">email: </LABEL>
              <INPUT type="text" id="email"><BR>
    <INPUT type="radio" name="sex" value="Male"> Male<BR>
    <INPUT type="radio" name="sex" value="Female"> Female<BR>
    <INPUT type="submit" value="Send"> <INPUT type="reset">
    </P>
 </FORM>

Note. This specification includes more detailed information about forms in
the subsections on form display issues.

17.2 Controls

Users interact with forms through named controls.

A control's "control name" is given by its name attribute. The scope of the
name attribute for a control within a FORM element is the FORM element.

Each control has both an initial value and a current value, both of which
are character strings. Please consult the definition of each control for
information about initial values and possible constraints on values imposed
by the control. In general, a control's "initial value" may be specified
with the control element's value attribute. However, the initial value of a
TEXTAREA element is given by its contents, and the initial value of an
OBJECT element in a form is determined by the object implementation (i.e.,
it lies outside the scope of this specification).

The control's "current value" is first set to the initial value. Thereafter,
the control's current value may be modified through user interaction and
scripts.

A control's initial value does not change. Thus, when a form is reset, each
control's current value is reset to its initial value. If a control does not
have an initial value, the effect of a form reset on that control is
undefined.

When a form is submitted for processing, some controls have their name
paired with their current value and these pairs are submitted with the form.
Those controls which name/value pairs are submitted are called successful
controls.

17.2.1 Control types

HTML defines the following control types:

buttons
     Authors may create three types of buttons:
        o submit buttons: When activated, a submit button submits a form. A
          form may contain more than one submit button.
        o reset buttons: When activated, a reset button resets all controls
          to their initial values.
        o push buttons: Push buttons have no default behavior. Each push
          button may have client-side scripts associated with the element's
          event attributes. When an event occurs (e.g., the user presses the
          button, releases it, etc.), the associated script is triggered.

          Authors should specify the scripting language of a push button
          script through a default script declaration (with the META
          element).

     Authors create buttons with the BUTTON element or the INPUT element.
     Please consult the definitions of these elements for details about
     specifying different button types.

     Note. Authors should note that the BUTTON element offers richer
     rendering capabilities than the INPUT element.
checkboxes
     Checkboxes (and radio buttons) are on/off switches that may be toggled
     by the user. A switch is "on" when the control element's selected
     attribute is set.

     When a form is submitted, only "on" checkbox controls can become
     successful. Several checkboxes in a form may share the same control
     name. Thus, for example, checkboxes allow users to select several
     values for the same property. The INPUT element is used to create a
     checkbox control.
radio buttons
     Radio buttons are like checkboxes except that when several share the
     same control name, they are mutually exclusive: when one is switched
     "on", all others with the same name are switched "off". The INPUT
     element is used to create a radio button control.
menus
     Menus offer users options from which to choose. The SELECT element
     creates a menu, in combination with the OPTGROUP and OPTION elements.
text input
     Authors may create two types of controls that allow users to input
     text. The INPUT element creates a single-line input control and the
     TEXTAREA element creates a multi-line input control. In both cases, the
     input text becomes the control's current value.
file select
     This control type allows the user to select files so that their
     contents may be submitted with a form. The INPUT element is used to
     create a file select control.
hidden controls
     Authors may create controls that are not rendered but whose values are
     submitted with a form. Authors generally use this control type to store
     information between client/server exchanges that would otherwise be
     lost due to the stateless nature of HTTP (see [RFC2068]). The INPUT
     element is used to create a hidden control.
object controls
     Authors may insert generic objects in forms such that associated values
     are submitted along with other controls. Authors create object controls
     with the OBJECT element.

The elements used to create controls generally appear inside a FORM element,
but may also appear outside of a FORM element declaration when they are used
to build user interfaces. This is discussed in the section on intrinsic
events. Note that controls outside a form cannot be successful controls.

17.3 The FORM element

<!ELEMENT FORM - - (%block;|SCRIPT)+ -(FORM) -- interactive form -->
<!ATTLIST FORM
  %attrs;                              -- %coreattrs, %i18n, %events --
  action      %URI;          #REQUIRED -- server-side form handler --
  method      (GET|POST)     GET       -- HTTP method used to submit the form--
  enctype     %ContentType;  "application/x-www-form-urlencoded"
  onsubmit    %Script;       #IMPLIED  -- the form was submitted --
  onreset     %Script;       #IMPLIED  -- the form was reset --
  accept-charset %Charsets;  #IMPLIED  -- list of supported charsets --
  >

Start tag: required, End tag: required

Attribute definitions

action = uri [CT]
     This attribute specifies a form processing agent. For example, the
     value might be a HTTP URI (to submit the form to a program) or a mailto
     URI (to email the form).
method = get|post [CI]
     This attribute specifies which HTTP method will be used to submit the
     form data set. Possible (case-insensitive) values are "get" (the
     default) and "post". See the section on form submission for usage
     information.
enctype = content-type [CI]
     This attribute specifies the content type used to submit the form to
     the server (when the value of method is "post"). The default value for
     this attribute is "application/x-www-form-urlencoded". The value
     "multipart/form-data" should be used in combination with the INPUT
     element, type="file".
accept-charset = charset list [CI]
     This attribute specifies the list of character encodings for input data
     that must be accepted by the server processing this form. The value is
     a space- and/or comma-delimited list of charset values. The server must
     interpret this list as an exclusive-or list, i.e., the server must be
     able to accept any single character encoding per entity received.

     The default value for this attribute is the reserved string "UNKNOWN".
     User agents may interpret this value as the character encoding that was
     used to transmit the document containing this FORM element.
accept = content-type-list [CI]
     This attribute specifies a comma-separated list of content types that a
     server processing this form will handle correctly. User agents may use
     this information to filter out non-conforming files when prompting a
     user to select files to be sent to the server (cf. the INPUT element
     when type="file").

Attributes defined elsewhere

   * id, class (document-wide identifiers)
   * lang (language information), dir (text direction)
   * style (inline style information)
   * title (element title)
   * target (target frame information)
   * onsubmit, onreset, onclick, ondblclick, onmousedown, onmouseup,
     onmouseover, onmousemove, onmouseout, onkeypress, onkeydown, onkeyup
     (intrinsic events)

The FORM element acts as a container for controls. It specifies:

   * The layout of the form (given by the contents of the element).
   * The program that will handle the completed and submitted form (the
     action attribute). The receiving program must be able to parse
     name/value pairs in order to make use of them.
   * The method by which user data will be sent to the server (the method
     attribute).
   * A character encoding that must be accepted by the server in order to
     handle this form (the accept-charset attribute). User agents may advise
     the user of the value of the accept-charset attribute and/or restrict
     the user's ability to enter unrecognized characters.

A form can contain text and markup (paragraphs, lists, etc.) in addition to
form controls.

The following example shows a form that is to be processed by the "adduser"
program when submitted. The form will be sent to the program using the HTTP
"post" method.

 <FORM action="http://somesite.com/prog/adduser" method="post">
 ...form contents...
 </FORM>

The next example shows how to send a submitted form to an email address:

 <FORM action="mailto:Kligor.T@gee.whiz.com" method="post">
 ...form contents...
 </FORM>

Please consult the section on form submission for information about how user
agents must prepare form data for servers and how user agents should handle
expected responses.

Note. Further discussion on the behavior of servers that receive form data
is beyond the scope of this specification.

17.4 The INPUT element

<!ENTITY % InputType
  "(TEXT | PASSWORD | CHECKBOX |
    RADIO | SUBMIT | RESET |
    FILE | HIDDEN | IMAGE | BUTTON)"
   >

<!-- attribute name required for all but submit & reset -->
<!ELEMENT INPUT - O EMPTY              -- form control -->
<!ATTLIST INPUT
  %attrs;                              -- %coreattrs, %i18n, %events --
  type        %InputType;    TEXT      -- what kind of widget is needed --
  name        CDATA          #IMPLIED  -- submit as part of form --
  value       CDATA          #IMPLIED  -- required for radio and checkboxes --
  checked     (checked)      #IMPLIED  -- for radio buttons and check boxes --
  disabled    (disabled)     #IMPLIED  -- unavailable in this context --
  readonly    (readonly)     #IMPLIED  -- for text and passwd --
  size        CDATA          #IMPLIED  -- specific to each type of field --
  maxlength   NUMBER         #IMPLIED  -- max chars for text fields --
  src         %URI;          #IMPLIED  -- for fields with images --
  alt         CDATA          #IMPLIED  -- short description --
  usemap      %URI;          #IMPLIED  -- use client-side image map --
  tabindex    NUMBER         #IMPLIED  -- position in tabbing order --
  accesskey   %Character;    #IMPLIED  -- accessibility key character --
  onfocus     %Script;       #IMPLIED  -- the element got the focus --
  onblur      %Script;       #IMPLIED  -- the element lost the focus --
  onselect    %Script;       #IMPLIED  -- some text was selected --
  onchange    %Script;       #IMPLIED  -- the element value was changed --
  accept      %ContentTypes; #IMPLIED  -- list of MIME types for file upload --
  >

Start tag: required, End tag: forbidden

Attribute definitions

type = text|password|checkbox|radio|submit|reset|file|hidden|image|button
[CI]
     This attribute specifies the type of control to create. The default
     value for this attribute is "text".
name = cdata [CI]
     This attribute assigns the control name.
value = cdata [CA]
     This attribute specifies the initial value of the control. It is
     optional except when the type attribute has the value "radio".
size = cdata [CN]
     This attribute tells the user agent the initial width of the control.
     The width is given in pixels except when type attribute has the value
     "text" or "password". In that case, its value refers to the (integer)
     number of characters.
maxlength = number [CN]
     When the type attribute has the value "text" or "password", this
     attribute specifies the maximum number of characters the user may
     enter. This number may exceed the specified size, in which case the
     user agent should offer a scrolling mechanism. The default value for
     this attribute is an unlimited number.
checked [CI]
     When the type attribute has the value "radio" or "checkbox", this
     boolean attribute specifies that the button is on. User agents must
     ignore this attribute for other control types.
src = uri [CT]
     When the type attribute has the value "image", this attribute specifies
     the location of the image to be used to decorate the graphical submit
     button.

Attributes defined elsewhere

   * id, class (document-wide identifiers)
   * lang (language information), dir (text direction)
   * title (element title)
   * style (inline style information)
   * alt (alternate text)
   * align (alignment)
   * accept (legal content types for a server)
   * readonly (read-only input controls)
   * disabled (disabled input controls)
   * tabindex (tabbing navigation)
   * accesskey (access keys)
   * usemap (client-side image maps)
   * onfocus, onblur, onselect, onchange, onclick, ondblclick, onmousedown,
     onmouseup, onmouseover, onmousemove, onmouseout, onkeypress, onkeydown,
     onkeyup (intrinsic events)

17.4.1 Control types created with INPUT

The control type defined by the INPUT element depends on the value of the
type attribute:

text
     Creates a single-line text input control.
password
     Like "text", but the input text is rendered in such a way as to hide
     the characters (e.g., a series of asterisks). This control type is
     often used for sensitive input such as passwords. Note that the current
     value is the text entered by the user, not the text rendered by the
     user agent.

     Note. Application designers should note that this mechanism affords
     only light security protection. Although the password is masked by user
     agents from casual observers, it is transmitted to the server in clear
     text, and may be read by anyone with low-level access to the network.
checkbox
     Creates a checkbox.
radio
     Creates a radio button.
submit
     Creates a submit button.
image
     Creates a graphical submit button. The value of the src attribute
     specifies the URI of the image that will decorate the button. For
     accessibility reasons, authors should provide alternate text for the
     image via the alt attribute.

     When a pointing device is used to click on the image, the form is
     submitted and the click coordinates passed to the server. The x value
     is measured in pixels from the left of the image, and the y value in
     pixels from the top of the image. The submitted data includes
     name.x=x-value and name.y=y-value where "name" is the value of the name
     attribute, and x-value and y-value are the x and y coordinate values,
     respectively.

     If the server takes different actions depending on the location
     clicked, users of non-graphical browsers will be disadvantaged. For
     this reason, authors should consider alternate approaches:

        o Use multiple submit buttons (each with its own image) in place of
          a single graphical submit button. Authors may use style sheets to
          control the positioning of these buttons.
        o Use a client-side image map together with scripting.
reset
     Creates a reset button.
button
     Creates a push button. User agents should use the value of the value
     attribute as the button's label.
hidden
     Creates a hidden control.
file
     Creates a file select control. User agents may use the value of the
     value attribute as the initial file name.

17.4.2 Examples of forms containing INPUT controls

The following sample HTML fragment defines a simple form that allows the
user to enter a first name, last name, email address, and gender. When the
submit button is activated, the form will be sent to the program specified
by the action attribute.

 <FORM action="http://somesite.com/prog/adduser" method="post">
    <P>
    First name: <INPUT type="text" name="firstname"><BR>
    Last name: <INPUT type="text" name="lastname"><BR>
    email: <INPUT type="text" name="email"><BR>
    <INPUT type="radio" name="sex" value="Male"> Male<BR>
    <INPUT type="radio" name="sex" value="Female"> Female<BR>
    <INPUT type="submit" value="Send"> <INPUT type="reset">
    </P>
 </FORM>

This form might be rendered as follows:

[An example form rendering.]

In the section on the LABEL element, we discuss marking up labels such as
"First name".

In this next example, the JavaScript function name verify is triggered when
the "onclick" event occurs:

<HEAD>
<META http-equiv="Content-Script-Type" content="text/javascript">
</HEAD>
<BODY>
 <FORM action="..." method="post">
    <P>
    <INPUT type="button" value="Click Me" onclick="verify()">
 </FORM>
</BODY>

Please consult the section on intrinsic events for more information about
scripting and events.

The following example shows how the contents of a user-specified file may be
submitted with a form. The user is prompted for his or her name and a list
of file names whose contents should be submitted with the form. By
specifying the enctype value of "multipart/form-data", each file's contents
will be packaged for submission in a separate section of a multipart
document.

<FORM action="http://server.dom/cgi/handle"
    enctype="multipart/form-data"
    method="post">
 <P>
 What is your name? <INPUT type="text" name="name_of_sender">
 What files are you sending? <INPUT type="file" name="name_of_files">
 </P>
</FORM>

17.5 The BUTTON element

<!ELEMENT BUTTON - -
     (%flow;)* -(A|%formctrl;|FORM|FIELDSET)
     -- push button -->
<!ATTLIST BUTTON
  %attrs;                              -- %coreattrs, %i18n, %events --
  name        CDATA          #IMPLIED
  value       CDATA          #IMPLIED  -- sent to server when submitted --
  type        (button|submit|reset) submit -- for use as form button --
  disabled    (disabled)     #IMPLIED  -- unavailable in this context --
  tabindex    NUMBER         #IMPLIED  -- position in tabbing order --
  accesskey   %Character;    #IMPLIED  -- accessibility key character --
  onfocus     %Script;       #IMPLIED  -- the element got the focus --
  onblur      %Script;       #IMPLIED  -- the element lost the focus --
  >

Start tag: required, End tag: required

Attribute definitions

name = cdata [CI]
     This attribute assigns the control name.
value = cdata [CS]
     This attribute assigns the initial value to the button.
type = submit|button|reset [CI]
     This attribute declares the type of the button. Possible values:
        o submit: Creates a submit button. This is the default value.
        o reset: Creates a reset button.
        o button: Creates a push button.

Attributes defined elsewhere

   * disabled (disabled input controls)
   * accesskey (access keys)
   * usemap (client-side image maps)
   * onfocus, onblur, onclick, ondblclick, onmousedown, onmouseup,
     onmouseover, onmousemove, onmouseout, onkeypress, onkeydown, onkeyup
     (intrinsic events)

Buttons created with the BUTTON element function just like buttons created
with the INPUT element, but they offer richer rendering possibilities: the
BUTTON element may have content. For example, a BUTTON element that contains
an image functions like and may resemble an INPUT element whose type is set
to "image", but the BUTTON element type allows content.

Visual user agents may render BUTTON buttons with relief and an up/down
motion when clicked, while they may render INPUT buttons as a "flat" images.

The following example expands a previous example, but creates submit and
reset buttons with BUTTON instead of INPUT. The buttons contain images by
way of the IMG element.

 <FORM action="http://somesite.com/prog/adduser" method="post">
    <P>
    First name: <INPUT type="text" name="firstname"><BR>
    Last name: <INPUT type="text" name="lastname"><BR>
    email: <INPUT type="text" name="email"><BR>
    <INPUT type="radio" name="sex" value="Male"> Male<BR>
    <INPUT type="radio" name="sex" value="Female"> Female<BR>
    <BUTTON name="submit" value="submit" type="submit">
    Send<IMG src="/icons/wow.gif" alt="wow"></BUTTON>
    <BUTTON name="reset" type="reset">
    Reset<IMG src="/icons/oops.gif" alt="oops"></BUTTON>
    </P>
 </FORM>

Recall that authors must provide alternate text for an IMG element.

It is illegal to associate an image map with an IMG that appears as the
contents of a BUTTON element.

ILLEGAL EXAMPLE:
The following is not legal HTML.

<BUTTON>
<IMG src="foo.gif" usemap="...">
</BUTTON>

17.6 The SELECT, OPTGROUP, and OPTION elements

<!ELEMENT SELECT - - (OPTGROUP|OPTION)+ -- option selector -->
<!ATTLIST SELECT
  %attrs;                              -- %coreattrs, %i18n, %events --
  name        CDATA          #IMPLIED  -- field name --
  size        NUMBER         #IMPLIED  -- rows visible --
  multiple    (multiple)     #IMPLIED  -- default is single selection --
  disabled    (disabled)     #IMPLIED  -- unavailable in this context --
  tabindex    NUMBER         #IMPLIED  -- position in tabbing order --
  onfocus     %Script;       #IMPLIED  -- the element got the focus --
  onblur      %Script;       #IMPLIED  -- the element lost the focus --
  onchange    %Script;       #IMPLIED  -- the element value was changed --
  >

Start tag: required, End tag: required

SELECT Attribute definitions

name = cdata [CI]
     This attribute assigns the control name.
size = number [CN]
     If a SELECT element is presented as a scrolled list box, this attribute
     specifies the number of rows in the list that should be visible at the
     same time. Visual user agents are not required to present a SELECT
     element as a list box; they may use any other mechanism, such as a
     drop-down menu.
multiple [CI]
     If set, this boolean attribute allows multiple selections. If not set,
     the SELECT element only permits single selections.

The SELECT element creates a menu. Each choice offered by the menu is
represented by an OPTION element. A SELECT element must contain at least one
OPTION element.

The OPTGROUP element allows authors to group choices logically. This is
particularly helpful when the user must choose from a long list of options;
groups of related choices are easier to grasp and remember than a single
long list of options. In HTML 4.0, all OPTGROUP elements must be specified
directly within a SELECT element (i.e., groups may not be nested).

17.6.1 Preselected options

Zero or more choices may be pre-selected for the user. User agents should
determine which choices are pre-selected as follows:

   * If no OPTION element has the selected attribute set, no options should
     be pre-selected.
   * If one OPTION element has the selected attribute set, it should be
     pre-selected.
   * If the SELECT element has the multiple attribute set and more than one
     OPTION element has the selected attribute set, they should all be
     pre-selected.
   * It is considered an error if more than one OPTION element has the
     selected attribute set and the SELECT element does not have the
     multiple attribute set. User agents may vary in how they handle this
     error, but should not pre-select more than one choice.

<!ELEMENT OPTGROUP - - (OPTION)+ -- option group -->
<!ATTLIST OPTGROUP
  %attrs;                              -- %coreattrs, %i18n, %events --
  disabled    (disabled)     #IMPLIED  -- unavailable in this context --
  label       %Text;         #REQUIRED -- for use in hierarchical menus --
  >

Start tag: required, End tag: required

OPTGROUP Attribute definitions

label = text [CS]
     This attribute specifies the label for the option group.

Attributes defined elsewhere

   * id, class (document-wide identifiers)
   * lang (language information), dir (text direction)
   * title (element title)
   * style (inline style information)
   * disabled (disabled input controls)
   * onfocus, onblur, onchange, onclick, ondblclick, onmousedown, onmouseup,
     onmouseover, onmousemove, onmouseout, onkeypress, onkeydown, onkeyup
     (intrinsic events)

Note. Implementors are advised that future versions of HTML may extend the
grouping mechanism to allow for nested groups (i.e., OPTGROUP elements may
nest). This will allow authors to represent a richer hierarchy of choices.

<!ELEMENT OPTION - O (#PCDATA)         -- selectable choice -->
<!ATTLIST OPTION
  %attrs;                              -- %coreattrs, %i18n, %events --
  selected    (selected)     #IMPLIED
  disabled    (disabled)     #IMPLIED  -- unavailable in this context --
  label       %Text;         #IMPLIED  -- for use in hierarchical menus --
  value       CDATA          #IMPLIED  -- defaults to element content --
  >

Start tag: required, End tag: optional

OPTION Attribute definitions

selected [CI]
     When set, this boolean attribute specifies that this option is
     pre-selected.
value = cdata [CS]
     This attribute specifies the initial value of the control. If this
     attribute is not set, the initial value is set to the contents of the
     OPTION element.
label = text [CS]
     This attribute allows authors to specify a shorter label for an option
     than the content of the OPTION element. When specified, user agents
     should use the value of this attribute rather than the content of the
     OPTION element as the option label.

Attributes defined elsewhere

   * id, class (document-wide identifiers)
   * lang (language information), dir (text direction)
   * title (element title)
   * style (inline style information)
   * disabled (disabled input controls)
   * onfocus, onblur, onchange, onclick, ondblclick, onmousedown, onmouseup,
     onmouseover, onmousemove, onmouseout, onkeypress, onkeydown, onkeyup
     (intrinsic events)

When rendering a menu choice, user agents should use the value of the label
attribute of the OPTION element as the choice. If this attribute is not
specified, user agents should use the contents of the OPTION element.

The label attribute of the OPTGROUP element specifies the label for a group
of choices.

In this example, we create a menu that allows the user to select which of
seven software components to install. The first and second components are
pre-selected but may be deselected by the user. The remaining components are
not pre-selected. The size attribute states that the menu should only have 4
rows even though the user may select from among 7 options. The other options
should be made available through a scrolling mechanism.

The SELECT is followed by submit and reset buttons.

<FORM action="http://somesite.com/prog/component-select" method="post">
   <P>
   <SELECT multiple size="4" name="component-select">
      <OPTION selected value="Component_1_a">Component_1</OPTION>
      <OPTION selected value="Component_1_b">Component_2</OPTION>
      <OPTION>Component_3</OPTION>
      <OPTION>Component_4</OPTION>
      <OPTION>Component_5</OPTION>
      <OPTION>Component_6</OPTION>
      <OPTION>Component_7</OPTION>
   </SELECT>
   <INPUT type="submit" value="Send"><INPUT type="reset">
   </P>
</FORM>

Only selected options will be successful (using the control name
"component-select"). Note that where the value attribute is set, it
determines the control's initial value, otherwise it's the element's
contents.

In this example we use the OPTGROUP element to group choices. The following
markup:

<FORM action="http://somesite.com/prog/someprog" method="post">
 <P>
 <SELECT name="ComOS">
     <OPTGROUP label="PortMaster 3">
       <OPTION label="3.7.1" value="pm3_3.7.1">PortMaster 3 with ComOS 3.7.1
       <OPTION label="3.7" value="pm3_3.7">PortMaster 3 with ComOS 3.7
       <OPTION label="3.5" value="pm3_3.5">PortMaster 3 with ComOS 3.5
     </OPTGROUP>
     <OPTGROUP label="PortMaster 2">
       <OPTION label="3.7" value="pm2_3.7">PortMaster 2 with ComOS 3.7
       <OPTION label="3.5" value="pm2_3.5">PortMaster 2 with ComOS 3.5
     </OPTGROUP>
     <OPTGROUP label="IRX">
       <OPTION label="3.7R" value="IRX_3.7R">IRX with ComOS 3.7R
       <OPTION label="3.5R" value="IRX_3.5R">IRX with ComOS 3.5R
     </OPTGROUP>
 </SELECT>
</FORM>

represents the following grouping:

  PortMaster 3
      3.7.1
      3.7
      3.5
  PortMaster 2
      3.7
      3.5
  IRX
      3.7R
      3.5R

Visual user agents may allow users to select from option groups through a
hierarchical menu or some other mechanism that reflects the structure of
choices.

A graphical user agent might render this as:

[A possible rendering of OPTGROUP]

This image shows a SELECT element rendered as cascading menus. The top label
of the menu displays the currently selected value (PortMaster 3, 3.7.1). The
user has unfurled two cascading menus, but has not yet selected the new
value (PortMaster 2, 3.7). Note that each cascading menu displays the label
of an OPTGROUP or OPTION element.

17.7 The TEXTAREA element

<!ELEMENT TEXTAREA - - (#PCDATA)       -- multi-line text field -->
<!ATTLIST TEXTAREA
  %attrs;                              -- %coreattrs, %i18n, %events --
  name        CDATA          #IMPLIED
  rows        NUMBER         #REQUIRED
  cols        NUMBER         #REQUIRED
  disabled    (disabled)     #IMPLIED  -- unavailable in this context --
  readonly    (readonly)     #IMPLIED
  tabindex    NUMBER         #IMPLIED  -- position in tabbing order --
  accesskey   %Character;    #IMPLIED  -- accessibility key character --
  onfocus     %Script;       #IMPLIED  -- the element got the focus --
  onblur      %Script;       #IMPLIED  -- the element lost the focus --
  onselect    %Script;       #IMPLIED  -- some text was selected --
  onchange    %Script;       #IMPLIED  -- the element value was changed --
  >

Start tag: required, End tag: required

Attribute definitions

name = cdata [CI]
     This attribute assigns the control name.
rows = number [CN]
     This attribute specifies the number of visible text lines. Users should
     be able to enter more lines than this, so user agents should provide
     some means to scroll through the contents of the control when the
     contents extend beyond the visible area.
cols = number [CN]
     This attribute specifies the visible width in average character widths.
     Users should be able to enter longer lines than this, so user agents
     should provide some means to scroll through the contents of the control
     when the contents extend beyond the visible area. User agents may wrap
     visible text lines to keep long lines visible without the need for
     scrolling.

Attributes defined elsewhere

   * id, class (document-wide identifiers)
   * lang (language information), dir (text direction)
   * title (element title)
   * style (inline style information)
   * readonly (read-only input controls)
   * disabled (disabled input controls)
   * tabindex (tabbing navigation)
   * onfocus, onblur, onselect, onchange, onclick, ondblclick, onmousedown,
     onmouseup, onmouseover, onmousemove, onmouseout, onkeypress, onkeydown,
     onkeyup (intrinsic events)

The TEXTAREA element creates a multi-line text input control. User agents
should use the contents of this element as the initial value of the control
and should render this text initially.

This example creates a TEXTAREA control that is 20 rows by 80 columns and
contains two lines of text initially. The TEXTAREA is followed by submit and
reset buttons.

<FORM action="http://somesite.com/prog/text-read" method="post">
   <P>
   <TEXTAREA name="thetext" rows="20" cols="80">
   First line of initial text.
   Second line of initial text.
   </TEXTAREA>
   <INPUT type="submit" value="Send"><INPUT type="reset">
   </P>
</FORM>

Setting the readonly attribute allows authors to display unmodifiable text
in a TEXTAREA. This differs from using standard marked-up text in a document
because the value of TEXTAREA is submitted with the form.

17.8 The ISINDEX element

ISINDEX is deprecated. This element creates a single-line text input
control. Authors should use the INPUT element to create text input controls.

See the Transitional DTD for the formal definition.

Attribute definitions

prompt = text [CS]
     Deprecated. This attribute specifies a prompt string for the input
     field.

Attributes defined elsewhere

   * id, class (document-wide identifiers)
   * lang (language information), dir (text direction)
   * title (element title)
   * style (inline style information)

The ISINDEX element creates a single-line text input control that allows any
number of characters. User agents may use the value of the prompt attribute
as a title for the prompt.

DEPRECATED EXAMPLE:
The following ISINDEX declaration:

<ISINDEX prompt="Enter your search phrase: ">

could be rewritten with INPUT as follows:

<FORM action="..." method="post">
<P>Enter your search phrase: <INPUT type="text"></P>
</FORM>

Semantics of ISINDEX. Currently, the semantics for ISINDEX are only
well-defined when the base URI for the enclosing document is an HTTP URI. In
practice, the input string is restricted to Latin-1 as there is no mechanism
for the URI to specify a different character set.

17.9 Labels

Some form controls automatically have labels associated with them (press
buttons) while most do not (text fields, checkboxes and radio buttons, and
menus).

For those controls that have implicit labels, user agents should use the
value of the value attribute as the label string.

The LABEL element is used to specify labels for controls that do not have
implicit labels,

17.9.1 The LABEL element

<!ELEMENT LABEL - - (%inline;)* -(LABEL) -- form field label text -->
<!ATTLIST LABEL
  %attrs;                              -- %coreattrs, %i18n, %events --
  for         IDREF          #IMPLIED  -- matches field ID value --
  accesskey   %Character;    #IMPLIED  -- accessibility key character --
  onfocus     %Script;       #IMPLIED  -- the element got the focus --
  onblur      %Script;       #IMPLIED  -- the element lost the focus --
  >

Start tag: required, End tag: required

Attribute definitions

for = idref [CS]
     This attribute explicitly associates the label being defined with
     another control. When present, the value of this attribute must be the
     same as the value of the id attribute of some other control in the same
     document. When absent, the label being defined is associated with the
     element's contents.

Attributes defined elsewhere

   * id, class (document-wide identifiers)
   * lang (language information), dir (text direction)
   * title (element title)
   * style (inline style information)
   * accesskey (access keys)
   * tabindex (tabbing navigation)
   * onfocus, onblur, onclick, ondblclick, onmousedown, onmouseup,
     onmouseover, onmousemove, onmouseout, onkeypress, onkeydown, onkeyup
     (intrinsic events)

The LABEL element may be used to attach information to controls. Each LABEL
element is associated with exactly one form control.

The for attribute associates a label with another control explicitly: the
value of the for attribute must be the same as the value of the id attribute
of the associated control element. More than one LABEL may be associated
with the same control by creating multiple references via the for attribute.

This example creates a table that is used to align two text input controls
and their associated labels. Each label is associated explicitly with one
text input:

<FORM action="..." method="post">
<TABLE>
  <TR>
    <TD><LABEL for="fname">First Name</LABEL>
    <TD><INPUT type="text" name="firstname" id="fname">
  <TR>
    <TD><LABEL for="lname">Last Name</LABEL>
    <TD><INPUT type="text" name="lastname" id="lname">
</TABLE>
</FORM>

This example extends a previous example form to include LABEL elements.

 <FORM action="http://somesite.com/prog/adduser" method="post">
    <P>
    <LABEL for="firstname">First name: </LABEL>
              <INPUT type="text" id="firstname"><BR>
    <LABEL for="lastname">Last name: </LABEL>
              <INPUT type="text" id="lastname"><BR>
    <LABEL for="email">email: </LABEL>
              <INPUT type="text" id="email"><BR>
    <INPUT type="radio" name="sex" value="Male"> Male<BR>
    <INPUT type="radio" name="sex" value="Female"> Female<BR>
    <INPUT type="submit" value="Send"> <INPUT type="reset">
    </P>
 </FORM>

To associate a label with another control implicitly, the control element
must be within the contents of the LABEL element. In this case, the LABEL
may only contain one control element. The label itself may be positioned
before or after the associated control.

In this example, we implicitly associate two labels with two text input
controls:

<FORM action="..." method="post">
<P>
<LABEL>
   First Name
   <INPUT type="text" name="firstname">
</LABEL>
<LABEL>
   <INPUT type="text" name="lastname">
   Last Name
</LABEL>
</P>
</FORM>

Note that this technique cannot be used when a table is being used for
layout, with the label in one cell and its associated control in another
cell.

When a LABEL element receives focus, it passes the focus on to its
associated control. See the section below on access keys for examples.

Labels may be rendered by user agents in a number of ways (e.g., visually,
read by speech synthesizers, etc.)

17.10 Adding structure to forms: the FIELDSET and LEGEND elements

<!--
  #PCDATA is to solve the mixed content problem,
  per specification only whitespace is allowed there!
 -->
<!ELEMENT FIELDSET - - (#PCDATA,LEGEND,(%flow;)*) -- form control group -->
<!ATTLIST FIELDSET
  %attrs;                              -- %coreattrs, %i18n, %events --
  >

<!ELEMENT LEGEND - - (%inline;)*       -- fieldset legend -->
<!ENTITY % LAlign "(top|bottom|left|right)">

<!ATTLIST LEGEND
  %attrs;                              -- %coreattrs, %i18n, %events --
  accesskey   %Character;    #IMPLIED  -- accessibility key character --
  >

Start tag: required, End tag: required

LEGEND Attribute definitions

align = top|bottom|left|right [CI]
     Deprecated. This attribute specifies the position of the legend with
     respect to the fieldset. Possible values:
        o top: The legend is at the top of the fieldset. This is the default
          value.
        o bottom: The legend is at the bottom of the fieldset.
        o left: The legend is at the left side of the fieldset.
        o right: The legend is at the right side of the fieldset.

Attributes defined elsewhere

   * id, class (document-wide identifiers)
   * lang (language information), dir (text direction)
   * title (element title)
   * style (inline style information)
   * accesskey (access keys)
   * onclick, ondblclick, onmousedown, onmouseup, onmouseover, onmousemove,
     onmouseout, onkeypress, onkeydown, onkeyup (intrinsic events)

The FIELDSET element allows authors to group thematically related controls
and labels. Grouping controls makes it easier for users to understand their
purpose while simultaneously facilitating tabbing navigation for visual user
agents and speech navigation for speech-oriented user agents. The proper use
of this element makes documents more accessible.

The LEGEND element allows authors to assign a caption to a FIELDSET. The
legend improves accessibility when the FIELDSET is rendered non-visually.

In this example, we create a form that one might fill out at the doctor's
office. It is divided into three sections: personal information, medical
history, and current medication. Each section contains controls for
inputting the appropriate information.

<FORM action="..." method="post">
 <P>
 <FIELDSET>
  <LEGEND>Personal Information</LEGEND>
  Last Name: <INPUT name="personal_lastname" type="text" tabindex="1">
  First Name: <INPUT name="personal_firstname" type="text" tabindex="2">
  Address: <INPUT name="personal_address" type="text" tabindex="3">
  ...more personal information...
 </FIELDSET>
 <FIELDSET>
  <LEGEND>Medical History</LEGEND>
  <INPUT name="history_illness"
         type="checkbox"
         value="Smallpox" tabindex="20"> Smallpox
  <INPUT name="history_illness"
         type="checkbox"
         value="Mumps" tabindex="21"> Mumps
  <INPUT name="history_illness"
         type="checkbox"
         value="Dizziness" tabindex="22"> Dizziness
  <INPUT name="history_illness"
         type="checkbox"
         value="Sneezing" tabindex="23"> Sneezing
  ...more medical history...
 </FIELDSET>
 <FIELDSET>
  <LEGEND>Current Medication</LEGEND>
  Are you currently taking any medication?
  <INPUT name="medication_now"
         type="radio"
         value="Yes" tabindex="35">Yes
  <INPUT name="medication_now"
         type="radio"
         value="No" tabindex="35">No

  If you are currently taking medication, please indicate
  it in the space below:
  <TEXTAREA name="current_medication"
            rows="20" cols="50"
            tabindex="40">
  </TEXTAREA>
 </FIELDSET>
</FORM>

Note that in this example, we might improve the visual presentation of the
form by aligning elements within each FIELDSET (with style sheets), adding
color and font information (with style sheets), adding scripting (say, to
only open the "current medication" text area if the user indicates he or she
is currently on medication), etc. /samp

17.11 Giving focus to an element

In an HTML document, an element must receive focus from the user in order to
become active and perform their tasks. For example, users must activate a
link specified by the A element in order to follow the specified link.
Similarly, users must give a TEXTAREA focus in order to enter text into it.

There are several ways to give focus to an element:

   * Designate the element with a pointing device.
   * Navigate from one element to the next with the keyboard. The document's
     author may define a tabbing order that specifies the order in which
     elements will receive focus if the user navigates the document with the
     keyboard (see tabbing navigation). Once selected, an element may be
     activated by some other key sequence.
   * Select an element through an access key (sometimes called "keyboard
     shortcut" or "keyboard accelerator").

17.11.1 Tabbing navigation

Attribute definitions

tabindex = number [CN]
     This attribute specifies the position of the current element in the
     tabbing order for the current document. This value must be a number
     between 0 and 32767. User agents should ignore leading zeros.

The tabbing order defines the order in which elements will receive focus
when navigated by the user via the keyboard. The tabbing order may include
elements nested within other elements.

Elements that may receive focus should be navigated by user agents according
to the following rules:

  1. Those elements that support the tabindex attribute and assign a
     positive value to it are navigated first. Navigation proceeds from the
     element with the lowest tabindex value to the element with the highest
     value. Values need not be sequential nor must they begin with any
     particular value. Elements that have identical tabindex values should
     be navigated in the order they appear in the character stream.
  2. Those elements that do not support the tabindex attribute or support it
     and assign it a value of "0" are navigated next. These elements are
     navigated in the order they appear in the character stream.
  3. Elements that are disabled do not participate in the tabbing order.

The following elements support the tabindex attribute: A, AREA, BUTTON,
INPUT, OBJECT, SELECT, and TEXTAREA.

In this example, the tabbing order will be the BUTTON, the INPUT elements in
order (note that "field1" and the button share the same tabindex, but
"field1" appears later in the character stream), and finally the link
created by the A element.

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0//EN"
   "http://www.w3.org/TR/REC-html40/strict.dtd">
<HTML>
<HEAD>
<TITLE>A document with FORM</TITLE>
</HEAD>
<BODY>
...some text...
<P>Go to the
<A tabindex="10" href="http://www.w3.org/">W3C Web site.</A>
...some more...
<BUTTON type="button" name="get-database"
           tabindex="1" onclick="get-database">
Get the current database.
</BUTTON>
...some more...
<FORM action="..." method="post">
<P>
<INPUT tabindex="1" type="text" name="field1">
<INPUT tabindex="2" type="text" name="field2">
<INPUT tabindex="3" type="submit" name="submit">
</P>
</FORM>
</BODY>
</HTML>

Tabbing keys. The actual key sequence that causes tabbing navigation or
element activation depends on the configuration of the user agent (e.g., the
"tab" key is used for navigation and the "enter" key is used to activate a
selected element).

User agents may also define key sequences to navigate the tabbing order in
reverse. When the end (or beginning) of the tabbing order is reached, user
agents may circle back to the beginning (or end).

17.11.2 Access keys

Attribute definitions

accesskey = character [CN]
     This attribute assigns an access key to an element. An access key is a
     single character from the document character set.Note. Authors should
     consider the input method of the expected reader when specifying an
     accesskey.

Pressing an access key assigned to an element gives focus to the element.
The action that occurs when an element receives focus depends on the
element. For example, when a user activates a link defined by the A element,
the user agent generally follows the link. When a user activates a radio
button, the user agent changes the value of the radio button. When the user
activates a text field, it allows input, etc.

The following elements support the accesskey attribute: A, AREA, BUTTON,
INPUT, LABEL, and LEGEND, and TEXTAREA.

This example assigns the access key "U" to a label associated with an INPUT
control. Typing the access key gives focus to the label which in turn gives
it to the associated control. The user may then enter text into the INPUT
area.

<FORM action="..." method="post">
<P>
<LABEL for="fuser" accesskey="U">
User Name
</LABEL>
<INPUT type="text" name="user" id="fuser">
</P>
</FORM>

In this example, we assign an access key to a link defined by the A element.
Typing this access key takes the user to another document, in this case, a
table of contents.

<P><A accesskey="C"
      rel="contents"
      href="http://someplace.com/specification/contents.html">
    Table of Contents</A>

The invocation of access keys depends on the underlying system. For
instance, on machines running MS Windows, one generally has to press the
"alt" key in addition to the access key. On Apple systems, one generally has
to press the "cmd" key in addition to the access key.

The rendering of access keys depends on the user agent. We recommend that
authors include the access key in label text or wherever the access key is
to apply. User agents should render the value of an access key in such a way
as to emphasize its role and to distinguish it from other characters (e.g.,
by underlining it).

17.12 Disabled and read-only controls

In contexts where user input is either undesirable or irrelevant, it is
important to be able to disable a control or render it read-only. For
example, one may want to disable a form's submit button until the user has
entered some required data. Similarly, an author may want to include a piece
of read-only text that must be submitted as a value along with the form. The
following sections describe disabled and read-only controls.

17.12.1 Disabled controls

Attribute definitions

disabled [CI]
     When set for a form control, this boolean attribute disables the
     control for user input.

When set, the disabled attribute has the following effects on an element:

   * Disabled controls do not receive focus.
   * Disabled controls are skipped in tabbing navigation.
   * Disabled controls cannot be successful.

The following elements support the disabled attribute: BUTTON INPUT,
OPTGROUP, OPTION, SELECT, and TEXTAREA.

This attribute is inherited but local declarations override the inherited
value.

How disabled elements are rendered depends on the user agent. For example,
some user agents "gray out" disabled menu items, button labels, etc.

In this example, the INPUT element is disabled. Therefore, it cannot receive
user input nor will its value be submitted with the form.

<INPUT disabled name="fred" value="stone">

Note. The only way to modify dynamically the value of the disabled attribute
is through a script.

17.12.2 Read-only controls

Attribute definitions

readonly [CI]
     When set for a form control, this boolean attribute prohibits changes
     to the control.

The readonly attribute specifies whether the control may be modified by the
user.

When set, the readonly attribute has the following effects on an element:

   * Read-only elements receive focus but cannot be modified by the user.
   * Read-only elements are included in tabbing navigation.
   * Read-only elements may be successful.

The following elements support the readonly attribute: INPUT, TEXT,
PASSWORD, and TEXTAREA.

How read-only elements are rendered depends on the user agent.

Note. The only way to modify dynamically the value of the readonly attribute
is through a script.

17.13 Form submission

The following sections explain how user agents submit form data to form
processing agents.

17.13.1 Form submission method

The method attribute of the FORM element specifies the HTTP method used to
send the form to the processing agent. This attribute may take two values:

   * get: With the HTTP "get" method, the form data set is appended to the
     URI specified by the action attribute and this new URI is sent to the
     processing agent.
   * post: With the HTTP "post" method, the form data set is included in the
     body of the form and sent to the processing agent.

The "get" method should be used when the form is idempotent (i.e., causes no
side-effects). Many database searches have no visible side-effects and make
ideal applications for the "get" method.

If the service associated with the processing of a form causes side effects
(for example, if the form modifies a database or subscription to a service),
the "post" method should be used.

Note. The "get" method restricts form data set values to ASCII characters.
Only the "post" method (with enctype="multipart/form-data") is specified to
cover the entire [ISO10646] character set.

17.13.2 Successful controls

A successful control is "valid" for submission. Every successful control has
its control name paired with its current value as part of the submitted form
data set. A successful control must be defined within a FORM element and
must have a control name.

However:

   * Controls that are disabled cannot be successful.
   * If a form contains more than one submit button, only the activated
     submit button is successful.
   * All "on" checkboxes may be successful.
   * For radio buttons that share the same value of the name attribute, only
     the "on" radio button may be successful.
   * For menus, the control name is provided by a SELECT element and values
     are provided by OPTION elements. Only selected options may be
     successful.
   * The current value of a file select is a list of one or more file names.
     Upon submission of the form, the contents of each file are submitted
     with the rest of the form data. The file contents are packaged
     according to the form's content type.
   * The current value of an object control is determined by the object's
     implementation.

If a control doesn't have a current value when the form is submitted, user
agents are not required to treat it as a successful control.

Furthermore, user agents should not consider the following controls
successful:

   * Reset buttons.
   * OBJECT elements whose declare attribute has been set.

Hidden controls and controls that are not rendered because of style sheet
settings may still be successful. For example:

<FORM action="..." method="post">
<P>
<INPUT type="password" style="display:none"
          name="invisible-password"
          value="mypassword">
</FORM>

will still cause a value to be paired with the name "invisible-password" and
submitted with the form.

17.13.3 Processing form data

When the user submits a form (e.g., by activating a submit button), the user
agent processes it as follows.

Step one: Identify the successful controls

Step two: Build a form data set

A form data set is a sequence of control-name/current-value pairs
constructed from successful controls

Step three: Encode the form data set

The form data set is then encoded according to the content type specified by
the enctype attribute of the FORM element.

Step four: Submit the encoded form data set

Finally, the encoded data is sent to the processing agent designated by the
action attribute using the protocol specified by the method attribute.

This specification does not specify all valid submission methods or content
types that may be used with forms. However, HTML 4.0 user agents must
support the established conventions in the following cases:

   * If the method is "get" and the action is an HTTP URI, the user agent
     takes the value of action, appends a `?' to it, then appends the form
     data set, encoded using the "application/x-www-form-urlencoded" content
     type. The user agent then traverses the link to this URI. In this
     scenario, form data are restricted to ASCII codes.
   * If the method is "post" and the action is an HTTP URI, the user agent
     conducts an HTTP "post" transaction using the value of the action
     attribute and a message created according to the content type specified
     by the enctype attribute.

For any other value of action or method, behavior is unspecified.

User agents should render the response from the HTTP "get" and "post"
transactions.

17.13.4 Form content types

The enctype attribute of the FORM element specifies the content type used to
encode the form data set for submission to the server. User agents must
support the content types listed below. Behavior for other content types is
unspecified.

Please also consult the section on escaping ampersands in URI attribute
values.

application/x-www-form-urlencoded

This is the default content type. Forms submitted with this content type
must be encoded as follows:

  1. Control names and values are escaped. Space characters are replaced by
     `+', and then reserved characters are escaped as described in
     [RFC1738], section 2.2: Non-alphanumeric characters are replaced by
     `%HH', a percent sign and two hexadecimal digits representing the ASCII
     code of the character. Line breaks are represented as "CR LF" pairs
     (i.e., `%0D%0A').
  2. The control names/values are listed in the order they appear in the
     document. The name is separated from the value by `=' and name/value
     pairs are separated from each other by `&'.

multipart/form-data

Note. Please consult [RFC1867] for additional information about file
uploads, including backwards compatibility issues, the relationship between
"multipart/form-data" and other content types, performance issues, etc.

Please consult the appendix for information about security issues for forms.

The content type "application/x-www-form-urlencoded" is inefficient for
sending large quantities of binary data or text containing non-ASCII
characters. The content type "multipart/form-data" should be used for
submitting forms that contain files, non-ASCII data, and binary data.

The content "multipart/form-data" follows the rules of all multipart MIME
data streams as outlined in [RFC2045]. The definition of
"multipart/form-data" is available at the [IANA] registry.

A "multipart/form-data" message contains a series of parts, each
representing a successful control. The parts are sent to the processing
agent in the same order the corresponding controls appear in the document
stream. Part boundaries should not occur in any of the data; how this is
done lies outside the scope of this specification.

As with all multipart MIME types, each part has an optional "Content-Type"
header that defaults to "text/plain". User agents should supply the
"Content-Type" header, accompanied by a "charset" parameter.

Each part is expected to contain:

  1. a "Content-Disposition" header whose value is "form-data".
  2. a name attribute specifying the control name of the corresponding
     control. Control names originally encoded in non-ASCII character sets
     may be encoded using the method outlined in [RFC2045].

Thus, for example, for a control named "mycontrol", the corresponding part
would be specified:

Content-Disposition: form-data; name="mycontrol"

As with all MIME transmissions, "CR LF" (i.e., `%0D%0A') is used to separate
lines of data.

Each part may be encoded and the "Content-Transfer-Encoding" header supplied
if the value of that part does not conform to the default (7BIT) encoding
(see [RFC2045], section 6)

If the contents of a file are submitted with a form, the file input should
be identified by the appropriate content type (e.g.,
"application/octet-stream"). If multiple files are to be returned as the
result of a single form entry, they should be returned as "multipart/mixed"
embedded within the "multipart/form-data".

The user agent should attempt to supply a file name for each submitted file.
The file name may be specified with the "filename" parameter of the
'Content-Disposition: form-data' header, or, in the case of multiple files,
in a 'Content-Disposition: file' header of the subpart. If the file name of
the client's operating system is not in US-ASCII, the file name might be
approximated or encoded using the method of [RFC2045]. This is convenient
for those cases where, for example, the uploaded files might contain
references to each other (e.g., a TeX file and its ".sty" auxiliary style
description).

The following example illustrates "multipart/form-data" encoding. Suppose we
have the following form:

 <FORM action="http://server.dom/cgi/handle"
       enctype="multipart/form-data"
       method="post">
   <P>
   What is your name? <INPUT type="text" name="submit-name"><BR>
   What files are you sending? <INPUT type="file" name="files"><BR>
   <INPUT type="submit" value="Send"> <INPUT type="reset">
 </FORM>

If the user enters "Larry" in the text input, and selects the text file
"file1.txt", the user agent might send back the following data:

   Content-Type: multipart/form-data; boundary=AaB03x

   --AaB03x
   Content-Disposition: form-data; name="submit-name"

   Larry
   --AaB03x
   Content-Disposition: form-data; name="files"; filename="file1.txt"
   Content-Type: text/plain

   ... contents of file1.txt ...
   --AaB03x--

If the user selected a second (image) file "file2.gif", the user agent might
construct the parts as follows:

   Content-Type: multipart/form-data; boundary=AaB03x

   --AaB03x
   Content-Disposition: form-data; name="submit-name"

   Larry
   --AaB03x
   Content-Disposition: form-data; name="files"
   Content-Type: multipart/mixed; boundary=BbC04y

   --BbC04y
   Content-Disposition: attachment; filename="file1.txt"
   Content-Type: text/plain

   ... contents of file1.txt ...
   --BbC04y
   Content-Disposition: attachment; filename="file2.gif"
   Content-Type: image/gif
   Content-Transfer-Encoding: binary

   ...contents of file2.gif...
   --BbC04y--
   --AaB03x--

                                 18 Scripts

Contents

  1. Introduction to scripts
  2. Designing documents for user agents that support scripting
       1. The SCRIPT element
       2. Specifying the scripting language
             + The default scripting language
             + Local declaration of a scripting language
             + References to HTML elements from a script
       3. Intrinsic events
       4. Dynamic modification of documents
  3. Designing documents for user agents that don't support scripting
       1. The NOSCRIPT element
       2. Hiding script data from user agents

18.1 Introduction to scripts

A client-side script is a program that may accompany an HTML document or be
embedded directly in it. The program executes on the client's machine when
the document loads, or at some other time such as when a link is activated.
HTML's support for scripts is independent of the scripting language.

Scripts offer authors a means to extend HTML documents in highly active and
interactive ways. For example:

   * Scripts may be evaluated as a document loads to modify the contents of
     the document dynamically.
   * Scripts may accompany a form to process input as it is entered.
     Designers may dynamically fill out parts of a form based on the values
     of other fields. They may also ensure that input data conforms to
     predetermined ranges of values, that fields are mutually consistent,
     etc.
   * Scripts may be triggered by events that affect the document, such as
     loading, unloading, element focus, mouse movement, etc.
   * Scripts may be linked to form controls (e.g., buttons) to produce
     graphical user interface elements.

There are two types of scripts authors may attach to an HTML document:

   * Those that are executed one time when the document is loaded by the
     user agent. Scripts that appear within a SCRIPT element are executed
     when the document is loaded. For user agents that cannot or will not
     handle scripts, authors may include alternate content via the NOSCRIPT
     element.
   * Those that are executed every time a specific event occurs. These
     scripts may be assigned to a number of elements via the intrinsic event
     attributes.

Note. This specification includes more detailed information about scripting
in sections on script macros.

18.2 Designing documents for user agents that support scripting

The following sections discuss issues that concern user agents that support
scripting.

18.2.1 The SCRIPT element

<!ELEMENT SCRIPT - - %Script;          -- script statements -->
<!ATTLIST SCRIPT
  charset     %Charset;      #IMPLIED  -- char encoding of linked resource --
  type        %ContentType;  #REQUIRED -- content type of script language --
  language    CDATA          #IMPLIED  -- predefined script language name --
  src         %URI;          #IMPLIED  -- URI for an external script --
  defer       (defer)        #IMPLIED  -- UA may defer execution of script --
  >

Start tag: required, End tag: required

Attribute definitions

src = uri [CT]
     This attribute specifies the location of an external script.
type = content-type [CI]
     This attribute specifies the scripting language of the element's
     contents and overrides the default scripting language. The scripting
     language is specified as a content type (e.g., "text/javascript").
     Authors must supply a value for this attribute. There is no default
     value for this attribute.
language = cdata [CI]
     Deprecated.This attribute specifies the scripting language of the
     contents of this element. Its value is an identifier for the language,
     but since these identifiers are not standard, this attribute has been
     deprecated in favor of type.
defer [CI]
     When set, this boolean attribute provides a hint to the user agent that
     the script is not going to generate any document content (e.g., no
     "document.write" in javascript) and thus, the user agent can continue
     parsing and rendering.

Attributes defined elsewhere

   * charset(character encodings)

The SCRIPT element places a script within a document. This element may
appear any number of times in the HEAD or BODY of an HTML document.

The script may be defined within the contents of the SCRIPT element or in an
external file. If the src attribute is not set, user agents must interpret
the contents of the element as the script. If the src has a URI value, user
agents must ignore the element's contents and retrieve the script via the
URI. Note that the charset attribute refers to the character encoding of the
script designated by the src attribute; it does not concern the content of
the SCRIPT element.

Scripts are evaluated by script engines that must be known to a user agent.

The syntax of script data depends on the scripting language.

18.2.2 Specifying the scripting language

As HTML does not rely on a specific scripting language, document authors
must explicitly tell user agents the language of each script. This may be
done either through a default declaration or a local declaration.

The default scripting language

Authors should specify the default scripting language for all scripts in a
document by including the following META declaration in the HEAD:

<META http-equiv="Content-Script-Type" content="type">

where "type" is an content type naming the scripting language. Examples of
values include "text/tcl", "text/javascript", "text/vbscript".

In the absence of a META declaration, the default can be set by a
"Content-Script-Type" HTTP header.

    Content-Script-Type: type

where "type" is again an content type naming the scripting language.

User agents should determine the default scripting language for a document
according to the following steps (highest to lowest priority):

  1. If any META declarations specify the "Content-Script-Type", the last
     one in the character stream determines the default scripting language.
  2. Otherwise, if any HTTP headers specify the "Content-Script-Type", the
     last one in the character stream determines the default scripting
     language.

Documents that do not specify a default scripting language information and
that contain elements that specify an intrinsic event script are incorrect.
User agents may still attempt to interpret incorrectly specified scripts but
are not required to. Authoring tools should generate default scripting
language information to help authors avoid creating incorrect documents.

Local declaration of a scripting language

It is also possible to specify the scripting language in each SCRIPT element
via the type attribute. In the absence of a default scripting language
specification, this attribute must be set on each SCRIPT element. When a
default scripting language has been specified, the type attribute overrides
it.

In this example, we declare the default scripting language to be "text/tcl".
We include one SCRIPT in the header, whose script is located in an external
file and is in the scripting language "text/vbscript". We also include one
SCRIPT in the body, which contains its own script written in
"text/javascript".

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0//EN"
     "http://www.w3.org/TR/REC-html40/strict.dtd">
<HTML>
<HEAD>
<TITLE>A document with SCRIPT</TITLE>
<META http-equiv="Content-Script-Type" content="text/tcl">
<SCRIPT type="text/vbscript" src="http://someplace.com/progs/vbcalc">
</SCRIPT>
</HEAD>
<BODY>
<SCRIPT type="text/javascript">
...some JavaScript...
</SCRIPT>
</BODY>
</HTML>

References to HTML elements from a script

Each scripting language has its own conventions for referring to HTML
objects from within a script. This specification does not define a standard
mechanism for referring to HTML objects.

However, scripts should refer to an element according to its assigned name.
Scripting engines should observe the following precedence rules when
identifying an element: a name attribute takes precedence over a id if both
are set. Otherwise, one or the other may be used.

18.2.3 Intrinsic events

Note. Authors of HTML documents are advised that changes are likely to occur
in realm of intrinsic events (e.g., how scripts are bound to events).
Research in this realm is carried on by members of the W3C Document Object
Model Working Group (see the W3C Web Site at http://www.w3.org/ for more
information).

Attribute definitions

onload = script [CT]
     The onload event occurs when the user agent finishes loading a window
     or all frames within a FRAMESET. This attribute may be used with BODY
     and FRAMESET elements.
onunload = script [CT]
     The onunload event occurs when the user agent removes a document from a
     window or frame. This attribute may be used with BODY and FRAMESET
     elements.
onclick = script [CT]
     The onclick event occurs when the pointing device button is clicked
     over an element. This attribute may be used with most elements.
ondblclick = script [CT]
     The ondblclick event occurs when the pointing device button is double
     clicked over an element. This attribute may be used with most elements.
onmousedown = script [CT]
     The onmousedown event occurs when the pointing device button is pressed
     over an element. This attribute may be used with most elements.
onmouseup = script [CT]
     The onmouseup event occurs when the pointing device button is released
     over an element. This attribute may be used with most elements.
onmouseover = script [CT]
     The onmouseover event occurs when the pointing device is moved onto an
     element. This attribute may be used with most elements.
onmousemove = script [CT]
     The onmousemove event occurs when the pointing device is moved while it
     is over an element. This attribute may be used with most elements.
onmouseout = script [CT]
     The onmouseout event occurs when the pointing device is moved away from
     an element. This attribute may be used with most elements.
onfocus = script [CT]
     The onfocus event occurs when an element receives focus either by the
     pointing device or by tabbing navigation. This attribute may be used
     with the following elements: LABEL, INPUT, SELECT, TEXTAREA, and
     BUTTON.
onblur = script [CT]
     The onblur event occurs when an element loses focus either by the
     pointing device or by tabbing navigation. It may be used with the same
     elements as onfocus.
onkeypress = script [CT]
     The onkeypress event occurs when a key is pressed and released over an
     element. This attribute may be used with most elements.
onkeydown = script [CT]
     The onkeydown event occurs when a key is pressed down over an element.
     This attribute may be used with most elements.
onkeyup = script [CT]
     The onkeyup event occurs when a key is released over an element. This
     attribute may be used with most elements.
onsubmit = script [CT]
     The onsubmit event occurs when a form is submitted. It only applies to
     the FORM element.
onreset = script [CT]
     The onreset event occurs when a form is reset. It only applies to the
     FORM element.
onselect = script [CT]
     The onselect event occurs when a user selects some text in a text
     field. This attribute may be used with the INPUT and TEXTAREA elements.
onchange = script [CT]
     The onchange event occurs when a control loses the input focus and its
     value has been modified since gaining focus. This attribute applies to
     the following elements: INPUT, SELECT, and TEXTAREA.

It is possible to associate an action with a certain number of events that
occur when a user interacts with a user agent. Each of the "intrinsic
events" listed above takes a value that is a script. The script is executed
whenever the event occurs for that element. The syntax of script data
depends on the scripting language.

Control elements such as INPUT, SELECT, BUTTON, TEXTAREA, and LABEL all
respond to certain intrinsic events. When these elements do not appear
within a form, they may be used to augment the graphical user interface of
the document.

For instance, authors may want to include press buttons in their documents
that do not submit a form but still communicate with a server when they are
activated.

The following examples show some possible control and user interface
behavior based on intrinsic events.

In the following example, userName is a required text field. When a user
attempts to leave the field, the onblur event calls a JavaScript function to
confirm that userName has an acceptable value.

<INPUT NAME="userName" onblur="validUserName(this.value)">

Here is another JavaScript example:

<INPUT NAME="num"
    onchange="if (!checkNum(this.value, 1, 10))
        {this.focus();this.select();} else {thanks()}"
    VALUE="0">

Here is a VBScript example of an event handler for a text field:

    <INPUT name="edit1" size="50">
    <SCRIPT type="text/vbscript">
      Sub edit1_changed()
        If edit1.value = "abc" Then
          button1.enabled = True
        Else
          button1.enabled = False
        End If
      End Sub
    </SCRIPT>

Here is the same example using Tcl:

    <INPUT name="edit1" size="50">
    <SCRIPT type="text/tcl">
      proc edit1_changed {} {
        if {[edit value] == abc} {
          button1 enable 1
        } else {
          button1 enable 0
        }
      }
      edit1 onChange edit1_changed
    </SCRIPT>

Here is a JavaScript example for event binding within a script. First,
here's a simple click handler:


<BUTTON type="button" name="mybutton" value="10">
<SCRIPT type="text/javascript">
      function my_onclick() {
         . . .
      }
    document.form.mybutton.onclick = my_onclick
 </SCRIPT>
 </BUTTON>

Here's a more interesting window handler:


<SCRIPT type="text/javascript">
      function my_onload() {
         . . .
      }

      var win = window.open("some/other/URI")
      if (win) win.onload = my_onload
</SCRIPT>

In Tcl this looks like:

 <SCRIPT type="text/tcl">
     proc my_onload {} {
       . . .
     }
     set win [window open "some/other/URI"]
     if {$win != ""} {
         $win onload my_onload
     }
 </SCRIPT>

Note that "document.write" or equivalent statements in intrinsic event
handlers create and write to a new document rather than modifying the
current one.

18.2.4 Dynamic modification of documents

Scripts that are executed when a document is loaded may be able to modify
the document's contents dynamically. The ability to do so depends on the
scripting language itself (e.g., the "document.write" statement in the HTML
object model supported by some vendors).

The dynamic modification of a document may be modeled as follows:

  1. All SCRIPT elements are evaluated in order as the document is loaded.
  2. All script constructs within a given SCRIPT element that generate SGML
     CDATA are evaluated. Their combined generated text is inserted in the
     document in place of the SCRIPT element.
  3. The generated CDATA is re-evaluated.

HTML documents are constrained to conform to the HTML DTD both before and
after processing any SCRIPT elements.

The following example illustrates how scripts may modify a document
dynamically. The following script:

 <TITLE>Test Document</TITLE>
 <SCRIPT type="text/javascript">
     document.write("<p><b>Hello World!<\/b>")
 </SCRIPT>

Has the same effect as this HTML markup:

 <TITLE>Test Document</TITLE>
 <P><B>Hello World!</B>

18.3 Designing documents for user agents that don't support scripting

The following sections discuss how authors may create documents that work
for user agents that don't support scripting.

18.3.1 The NOSCRIPT element

<!ELEMENT NOSCRIPT - - (%block;)+
  -- alternate content container for non script-based rendering -->
<!ATTLIST NOSCRIPT
  %attrs;                              -- %coreattrs, %i18n, %events --
  >

Start tag: required, End tag: required

The NOSCRIPT element allows authors to provide alternate content when a
script is not executed. The content of a NOSCRIPT element should only
rendered by a script-aware user agent in the following cases:

   * The user agent is configured not to evaluate scripts.
   * The user agent doesn't support a scripting language invoked by a SCRIPT
     element earlier in the document.

User agents that do not support client-side scripts must render this
element's contents.

In the following example, a user agent that executes the SCRIPT will include
some dynamically created data in the document. If the user agent doesn't
support scripts, the user may still retrieve the data through a link.

<SCRIPT type="text/tcl">
 ...some Tcl script to insert data...
</SCRIPT>
<NOSCRIPT>
 <P>Access the <A href="http://someplace.com/data">data.</A>
</NOSCRIPT>

18.3.2 Hiding script data from user agents

User agents that don't recognize the SCRIPT element will likely render that
element's contents as text. Some scripting engines, including those for
languages JavaScript, VBScript, and Tcl allow the script statements to be
enclosed in an SGML comment. User agents that don't recognize the SCRIPT
element will thus ignore the comment while smart scripting engines will
understand that the script in comments should be executed.

Another solution to the problem is to keep scripts in external documents and
refer to them with the src attribute.

Commenting scripts in JavaScript
The JavaScript engine allows the string "<!--" to occur at the start of a
SCRIPT element, and ignores further characters until the end of the line.
JavaScript interprets "//" as starting a comment extending to the end of the
current line. This is needed to hide the string "-->" from the JavaScript
parser.

<SCRIPT type="text/javascript">
<!--  to hide script contents from old browsers
  function square(i) {
    document.write("The call passed ", i ," to the function.","<BR>")
    return i * i
  }
  document.write("The function returned ",square(5),".")
// end hiding contents from old browsers  -->
</SCRIPT>

Commenting scripts in VBScript
In VBScript, a single quote character causes the rest of the current line to
be treated as a comment. It can therefore be used to hide the string "-->"
from VBScript, for instance:

   <SCRIPT type="text/vbscript">
     <!--
       Sub foo()
        ...
       End Sub
     ' -->
    </SCRIPT>

Commenting scripts in TCL
In Tcl, the "#" character comments out the rest of the line:

<SCRIPT type="text/tcl">
<!--  to hide script contents from old browsers
  proc square {i} {
    document write "The call passed $i to the function.<BR>"
    return [expr $i * $i]
  }
  document write "The function returned [square 5]."
# end hiding contents from old browsers  -->
</SCRIPT>

Note. Some browsers close comments on the first ">" character, so to hide
script content from such browsers, you can transpose operands for relational
and shift operators (e.g., use "y < x" rather than "x > y") or use scripting
language-dependent escapes for ">".

                   19 SGML reference information for HTML

Contents

  1. document Document Validation
  2. Sample SGML catalog

The following sections contain the formal SGML definition of HTML 4.0. It
includes the SGML declaration, the Document Type Definition (DTD), and the
Character entity references, as well as a sample SGML catalog.

These files are also available in ASCII format as listed below:

Default DTD:
     http://www.w3.org/TR/REC-html40/strict.dtd
Transitional DTD:
     http://www.w3.org/TR/REC-html40/loose.dtd
Frameset DTD:
     http://www.w3.org/TR/REC-html40/frameset.dtd
SGML declaration:
     http://www.w3.org/TR/REC-html40/HTML4.decl
Entity definition files:
     http://www.w3.org/TR/REC-html40/HTMLspecial.ent
     http://www.w3.org/TR/REC-html40/HTMLsymbol.ent
     http://www.w3.org/TR/REC-html40/HTMLlat1.ent
A sample catalog:
     http://www.w3.org/TR/REC-html40/HTML4.cat

19.1 document Document Validation

Many authors rely on a limited set of browsers to check on the documents
they produce, assuming that if the browsers can render their documents they
are valid. Unfortunately, this is a very ineffective means of verifying a
document's validity precisely because browsers are designed to cope with
invalid documents by rendering them as well as they can to avoid frustrating
users.

For better validation, you should check your document against an SGML parser
such as nsgmls (see [SP]), to verify that HTML documents conform to the HTML
4.0 DTD. If the document type declaration of your document includes a URI
and your SGML parser supports this type of system identifier, it will get
the DTD directly. Otherwise you can use the following sample SGML catalog.
It assumes that the DTD has been saved as the file "strict.dtd" and that the
entities are in the files "HTMLlat1.ent", "HTMLsymbol.ent" and
"HTMLspecial.ent". In any case, make sure your SGML parser is capable of
handling Unicode. See your validation tool documentation for further
details.

Beware that such validation, although useful and highly recommended, does
not guarantee that a document fully conforms to the HTML 4.0 specification.
This is because an SGML parser relies solely on the given SGML DTD which
does not express all aspects of a valid HTML 4.0 document. Specifically, an
SGML parser ensures that the syntax, the structure, the list of elements,
and their attributes are valid. But for instance, it cannot catch errors
such as setting the width attribute of an IMG element to an invalid value
(i.e., "foo" or "12.5"). Although the specification restricts the value for
this attribute to an "integer representing a length in pixels," the DTD only
defines it to be CDATA, which actually allows any value. Only a specialized
program could capture the complete specification of HTML 4.0.

Nevertheless, this type of validation is still highly recommended since it
permits the detection of a large set of errors that make documents invalid.

19.2 Sample SGML catalog

This catalog includes the override directive to ensure that processing
software such as nsgmls uses public identifiers in preference to system
identifiers. This means that users do not have to be connected to the Web
when retrieving URI-based system identifiers.

OVERRIDE YES

PUBLIC "-//W3C//DTD HTML 4.0//EN" strict.dtd
PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" loose.dtd
PUBLIC "-//W3C//DTD HTML 4.0 Frameset//EN" frameset.dtd
PUBLIC "-//W3C//ENTITIES Latin1//EN//HTML" HTMLlat1.ent
PUBLIC "-//W3C//ENTITIES Special//EN//HTML" HTMLspecial.ent
PUBLIC "-//W3C//ENTITIES Symbols//EN//HTML" HTMLsymbol.ent

                       20 SGML Declaration of HTML 4.0

Note. The total number of codepoints allowed in the document character set
of this SGML declaration includes the first 17 planes of [ISO10646] (17
times 65536). This limitation has been made because this number is limited
to a length of 8 digits in the current version of the SGML standard. It does
not imply any statement about the feasibility of a long-term restriction of
characters in UCS to the first 17 planes. Chances are very high that the
limitation to 8 digits in SGML will be removed before, and that this
specification will be updated before, the first assignment of a character
beyond the first 17 planes.

Note. Strictly speaking, ISO Registration Number 177 refers to the original
state of [ISO10646] in 1993, while in this specification, we always refer to
the most up-to-date form of ISO 10646. Changes since 1993 have been the
addition of characters and a one-time operation reallocating a large number
of codepoints for Korean Hangul (Amendment 5).

20.1 SGML Declaration

<!SGML  "ISO 8879:1986"
    --
         SGML Declaration for HyperText Markup Language version 4.0

         With support for the first 17 planes of ISO 10646 and
         increased limits for tag and literal lengths etc.
    --

    CHARSET
          BASESET  "ISO Registration Number 177//CHARSET
                    ISO/IEC 10646-1:1993 UCS-4 with
                    implementation level 3//ESC 2/5 2/15 4/6"
         DESCSET 0       9       UNUSED
                 9       2       9
                 11      2       UNUSED
                 13      1       13
                 14      18      UNUSED
                 32      95      32
                 127     1       UNUSED
                 128     32      UNUSED
                 160     55136   160
                 55296   2048    UNUSED  -- SURROGATES --
                 57344   1056768 57344

CAPACITY        SGMLREF
                TOTALCAP        150000
                GRPCAP          150000
                ENTCAP          150000

SCOPE    DOCUMENT
SYNTAX
         SHUNCHAR CONTROLS 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
           17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 127
         BASESET  "ISO 646IRV:1991//CHARSET
                   International Reference Version
                   (IRV)//ESC 2/8 4/2"
         DESCSET  0 128 0

         FUNCTION
                  RE            13
                  RS            10
                  SPACE         32
                  TAB SEPCHAR    9

         NAMING   LCNMSTRT ""
                  UCNMSTRT ""
                  LCNMCHAR ".-_:"
                  UCNMCHAR ".-_:"
                  NAMECASE GENERAL YES
                           ENTITY  NO
         DELIM    GENERAL  SGMLREF
                  SHORTREF SGMLREF
         NAMES    SGMLREF
         QUANTITY SGMLREF
                  ATTCNT   60      -- increased --
                  ATTSPLEN 65536   -- These are the largest values --
                  LITLEN   65536   -- permitted in the declaration --
                  NAMELEN  65536   -- Avoid fixed limits in actual --
                  PILEN    65536   -- implementations of HTML UA's --
                  TAGLVL   100
                  TAGLEN   65536
                  GRPGTCNT 150
                  GRPCNT   64

FEATURES
  MINIMIZE
    DATATAG  NO
    OMITTAG  YES
    RANK     NO
    SHORTTAG YES
  LINK
    SIMPLE   NO
    IMPLICIT NO
    EXPLICIT NO
  OTHER
    CONCUR   NO
    SUBDOC   NO
    FORMAL   YES
  APPINFO NONE
>

                        21 Document Type Definition

<!--
    This is HTML 4.0 Strict DTD, which excludes the presentation
    attributes and elements that W3C expects to phase out as
    support for style sheets matures. Authors should use the Strict
    DTD when possible, but may use the Transitional DTD when support
    for presentation attribute and elements is required.

    HTML 4.0 includes mechanisms for style sheets, scripting,
    embedding objects, improved support for right to left and mixed
    direction text, and enhancements to forms for improved
    accessibility for people with disabilities.

          Draft: $Date: 1997/12/18 09:36:02 $

          Authors:
              Dave Raggett <dsr@w3.org>
              Arnaud Le Hors <lehors@w3.org>
              Ian Jacobs <ij@w3.org>

    Further information about HTML 4.0 is available at:

        http://www.w3.org/TR/REC-html40
-->
<!--
    Typical usage:

    <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0//EN"
            "http://www.w3.org/TR/REC-html40/strict.dtd">
    <html>
    <head>
    ...
    </head>
    <body>
    ...
    </body>
    </html>

    The URI used as a system identifier with the public identifier allows
    the user agent to download the DTD and entity sets as needed.

    The FPI for the Transitional HTML 4.0 DTD is:

        "-//W3C//DTD HTML 4.0 Transitional//EN

    and its URI is:

        http://www.w3.org/TR/REC-html40/loose.dtd

    If you are writing a document that includes frames, use
    the following FPI:

        "-//W3C//DTD HTML 4.0 Frameset//EN"

    with the URI:

        http://www.w3.org/TR/REC-html40/frameset.dtd

    The following URIs are supported in relation to HTML 4.0

    "http://www.w3.org/TR/REC-html40/strict.dtd" (Strict DTD)
    "http://www.w3.org/TR/REC-html40/loose.dtd" (Loose DTD)
    "http://www.w3.org/TR/REC-html40/frameset.dtd" (Frameset DTD)
    "http://www.w3.org/TR/REC-html40/HTMLlat1.ent" (Latin-1 entities)
    "http://www.w3.org/TR/REC-html40/HTMLsymbol.ent" (Symbol entities)
    "http://www.w3.org/TR/REC-html40/HTMLspecial.ent" (Special entities)

    These URIs point to the latest version of each file. To reference
    this specific revision use the following URIs:

    "http://www.w3.org/TR/REC-html40-971218/strict.dtd"
    "http://www.w3.org/TR/REC-html40-971218/loose.dtd"
    "http://www.w3.org/TR/REC-html40-971218/frameset.dtd"
    "http://www.w3.org/TR/REC-html40-971218/HTMLlat1.ent"
    "http://www.w3.org/TR/REC-html40-971218/HTMLsymbol.ent"
    "http://www.w3.org/TR/REC-html40-971218/HTMLspecial.ent"

-->

<!--================== Imported Names ====================================-->

<!ENTITY % ContentType "CDATA"
    -- media type, as per [RFC2045]
    -->

<!ENTITY % ContentTypes "CDATA"
    -- comma-separated list of media types, as per [RFC2045]
    -->

<!ENTITY % Charset "CDATA"
    -- a character encoding, as per [RFC2045]
    -->

<!ENTITY % Charsets "CDATA"
    -- a space separated list of character encodings, as per [RFC2045]
    -->

<!ENTITY % LanguageCode "NAME"
    -- a language code, as per [RFC1766]
    -->

<!ENTITY % Character "CDATA"
    -- a single character from [ISO10646]
    -->

<!ENTITY % LinkTypes "CDATA"
    -- space-separated list of link types
    -->

<!ENTITY % MediaDesc "CDATA"
    -- single or comma-separated list of media descriptors
    -->

<!ENTITY % URI "CDATA"
    -- a Uniform Resource Identifier,
       see [URI]
    -->

<!ENTITY % Datetime "CDATA" -- date and time information. ISO date format -->

<!ENTITY % Script "CDATA" -- script expression -->

<!ENTITY % StyleSheet "CDATA" -- style sheet data -->

<!ENTITY % Text "CDATA">

<!-- Parameter Entities -->

<!ENTITY % head.misc "SCRIPT|STYLE|META|LINK|OBJECT" -- repeatable head elements -->

<!ENTITY % heading "H1|H2|H3|H4|H5|H6">

<!ENTITY % list "UL | OL">

<!ENTITY % preformatted "PRE">

<!--================ Character mnemonic entities =========================-->

<!ENTITY % HTMLlat1 PUBLIC
   "-//W3C//ENTITIES Latin1//EN//HTML"
   "http://www.w3.org/TR/REC-html40-971218/HTMLlat1.ent">
%HTMLlat1;

<!ENTITY % HTMLsymbol PUBLIC
   "-//W3C//ENTITIES Symbols//EN//HTML"
   "http://www.w3.org/TR/REC-html40-971218/HTMLsymbol.ent">
%HTMLsymbol;

<!ENTITY % HTMLspecial PUBLIC
   "-//W3C//ENTITIES Special//EN//HTML"
   "http://www.w3.org/TR/REC-html40-971218/HTMLspecial.ent">
%HTMLspecial;
<!--=================== Generic Attributes ===============================-->

<!ENTITY % coreattrs
 "id          ID             #IMPLIED  -- document-wide unique id --
  class       CDATA          #IMPLIED  -- space separated list of classes --
  style       %StyleSheet;   #IMPLIED  -- associated style info --
  title       %Text;         #IMPLIED  -- advisory title/amplification --"
  >

<!ENTITY % i18n
 "lang        %LanguageCode; #IMPLIED  -- language code --
  dir         (ltr|rtl)      #IMPLIED  -- direction for weak/neutral text --"
  >

<!ENTITY % events
 "onclick     %Script;       #IMPLIED  -- a pointer button was clicked --
  ondblclick  %Script;       #IMPLIED  -- a pointer button was double clicked--
  onmousedown %Script;       #IMPLIED  -- a pointer button was pressed down --
  onmouseup   %Script;       #IMPLIED  -- a pointer button was released --
  onmouseover %Script;       #IMPLIED  -- a pointer was moved onto --
  onmousemove %Script;       #IMPLIED  -- a pointer was moved within --
  onmouseout  %Script;       #IMPLIED  -- a pointer was moved away --
  onkeypress  %Script;       #IMPLIED  -- a key was pressed and released --
  onkeydown   %Script;       #IMPLIED  -- a key was pressed down --
  onkeyup     %Script;       #IMPLIED  -- a key was released --"
  >

<!-- Reserved Feature Switch -->
<!ENTITY % HTML.Reserved "IGNORE">

<!-- The following attributes are reserved for possible future use -->
<![ %HTML.Reserved; [
<!ENTITY % reserved
 "datasrc     %URI;          #IMPLIED  -- a single or tabular Data Source --
  datafld     CDATA          #IMPLIED  -- the property or column name --
  dataformatas (plaintext|html) plaintext -- text or html --"
  >
]]>

<!ENTITY % reserved "">

<!ENTITY % attrs "%coreattrs; %i18n; %events;">

<!--=================== Text Markup ======================================-->

<!ENTITY % fontstyle
 "TT | I | B | BIG | SMALL">

<!ENTITY % phrase "EM | STRONG | DFN | CODE |
                   SAMP | KBD | VAR | CITE | ABBR | ACRONYM" >

<!ENTITY % special
   "A | IMG | OBJECT | BR | SCRIPT | MAP | Q | SUB | SUP | SPAN | BDO">

<!ENTITY % formctrl "INPUT | SELECT | TEXTAREA | LABEL | BUTTON">

<!-- %inline; covers inline or "text-level" elements -->
<!ENTITY % inline "#PCDATA | %fontstyle; | %phrase; | %special; | %formctrl;">

<!ELEMENT (%fontstyle;|%phrase;) - - (%inline;)*>
<!ATTLIST (%fontstyle;|%phrase;)
  %attrs;                              -- %coreattrs, %i18n, %events --
  >

<!ELEMENT (SUB|SUP) - - (%inline;)*    -- subscript, superscript -->
<!ATTLIST (SUB|SUP)
  %attrs;                              -- %coreattrs, %i18n, %events --
  >

<!ELEMENT SPAN - - (%inline;)*         -- generic language/style container -->
<!ATTLIST SPAN
  %attrs;                              -- %coreattrs, %i18n, %events --
  %reserved;                           -- reserved for possible future use --
  >

<!ELEMENT BDO - - (%inline;)*          -- I18N BiDi over-ride -->
<!ATTLIST BDO
  %coreattrs;                          -- id, class, style, title --
  lang        %LanguageCode; #IMPLIED  -- language code --
  dir         (ltr|rtl)      #REQUIRED -- directionality --
  >

<!ELEMENT BR - O EMPTY                 -- forced line break -->
<!ATTLIST BR
  %coreattrs;                          -- id, class, style, title --
  >

<!--================== HTML content models ===============================-->

<!--
    HTML has two basic content models:

        %inline;     character level elements and text strings
        %block;      block-like elements e.g. paragraphs and lists
-->

<!ENTITY % block
     "P | %heading; | %list; | %preformatted; | DL | DIV | NOSCRIPT |
      BLOCKQUOTE | FORM | HR | TABLE | FIELDSET | ADDRESS">

<!ENTITY % flow "%block; | %inline;">

<!--=================== Document Body ====================================-->

<!ELEMENT BODY O O (%block;|SCRIPT)+ +(INS|DEL) -- document body -->
<!ATTLIST BODY
  %attrs;                              -- %coreattrs, %i18n, %events --
  onload          %Script;   #IMPLIED  -- the document has been loaded --
  onunload        %Script;   #IMPLIED  -- the document has been removed --
  >

<!ELEMENT ADDRESS - - (%inline;)* -- information on author -->
<!ATTLIST ADDRESS
  %attrs;                              -- %coreattrs, %i18n, %events --
  >

<!ELEMENT DIV - - (%flow;)*            -- generic language/style container -->
<!ATTLIST DIV
  %attrs;                              -- %coreattrs, %i18n, %events --
  %reserved;                           -- reserved for possible future use --
  >

<!--================== The Anchor Element ================================-->

<!ENTITY % Shape "(rect|circle|poly|default)">
<!ENTITY % Coords "CDATA" -- comma separated list of lengths -->

<!ELEMENT A - - (%inline;)* -(A)       -- anchor -->
<!ATTLIST A
  %attrs;                              -- %coreattrs, %i18n, %events --
  charset     %Charset;      #IMPLIED  -- char encoding of linked resource --
  type        %ContentType;  #IMPLIED  -- advisory content type --
  name        CDATA          #IMPLIED  -- named link end --
  href        %URI;          #IMPLIED  -- URI for linked resource --
  hreflang    %LanguageCode; #IMPLIED  -- language code --
  rel         %LinkTypes;    #IMPLIED  -- forward link types --
  rev         %LinkTypes;    #IMPLIED  -- reverse link types --
  accesskey   %Character;    #IMPLIED  -- accessibility key character --
  shape       %Shape;        rect      -- for use with client-side image maps --
  coords      %Coords;       #IMPLIED  -- for use with client-side image maps --
  tabindex    NUMBER         #IMPLIED  -- position in tabbing order --
  onfocus     %Script;       #IMPLIED  -- the element got the focus --
  onblur      %Script;       #IMPLIED  -- the element lost the focus --
  >

<!--================== Client-side image maps ============================-->

<!-- These can be placed in the same document or grouped in a
     separate document although this isn't yet widely supported -->

<!ELEMENT MAP - - ((%block;)+ | AREA+) -- client-side image map -->
<!ATTLIST MAP
  %attrs;                              -- %coreattrs, %i18n, %events --
  name        CDATA          #REQUIRED -- for reference by usemap --
  >

<!ELEMENT AREA - O EMPTY               -- client-side image map area -->
<!ATTLIST AREA
  %attrs;                              -- %coreattrs, %i18n, %events --
  shape       %Shape;        rect      -- controls interpretation of coords --
  coords      %Coords;       #IMPLIED  -- comma separated list of lengths --
  href        %URI;          #IMPLIED  -- URI for linked resource --
  nohref      (nohref)       #IMPLIED  -- this region has no action --
  alt         %Text;         #REQUIRED -- short description --
  tabindex    NUMBER         #IMPLIED  -- position in tabbing order --
  accesskey   %Character;    #IMPLIED  -- accessibility key character --
  onfocus     %Script;       #IMPLIED  -- the element got the focus --
  onblur      %Script;       #IMPLIED  -- the element lost the focus --
  >

<!--================== The LINK Element ==================================-->

<!--
  Relationship values can be used in principle:

   a) for document specific toolbars/menus when used
      with the LINK element in document head e.g.
        start, contents, previous, next, index, end, help
   b) to link to a separate style sheet (rel=stylesheet)
   c) to make a link to a script (rel=script)
   d) by stylesheets to control how collections of
      html nodes are rendered into printed documents
   e) to make a link to a printable version of this document
      e.g. a postscript or pdf version (rel=alternate media=print)
-->

<!ELEMENT LINK - O EMPTY               -- a media-independent link -->
<!ATTLIST LINK
  %attrs;                              -- %coreattrs, %i18n, %events --
  charset     %Charset;      #IMPLIED  -- char encoding of linked resource --
  href        %URI;          #IMPLIED  -- URI for linked resource --
  hreflang    %LanguageCode; #IMPLIED  -- language code --
  type        %ContentType;  #IMPLIED  -- advisory content type --
  rel         %LinkTypes;    #IMPLIED  -- forward link types --
  rev         %LinkTypes;    #IMPLIED  -- reverse link types --
  media       %MediaDesc;    #IMPLIED  -- for rendering on these media --
  >

<!--=================== Images ===========================================-->

<!-- Length defined in strict DTD for cellpadding/cellspacing -->
<!ENTITY % Length "CDATA" -- nn for pixels or nn% for percentage length -->
<!ENTITY % MultiLength "CDATA" -- pixel, percentage, or relative -->

<!ENTITY % MultiLengths "CDATA" -- comma-separated list of MultiLength -->

<!ENTITY % Pixels "CDATA" -- integer representing length in pixels -->

<!-- To avoid problems with text-only UAs as well as
   to make image content understandable and navigable
   to users of non-visual UAs, you need to provide
   a description with ALT, and avoid server-side image maps -->
<!ELEMENT IMG - O EMPTY                -- Embedded image -->
<!ATTLIST IMG
  %attrs;                              -- %coreattrs, %i18n, %events --
  src         %URI;          #REQUIRED -- URI of image to embed --
  alt         %Text;         #REQUIRED -- short description --
  longdesc    %URI;          #IMPLIED  -- link to long description
                                          (complements alt) --
  height      %Length;       #IMPLIED  -- override height --
  width       %Length;       #IMPLIED  -- override width --
  usemap      %URI;          #IMPLIED  -- use client-side image map --
  ismap       (ismap)        #IMPLIED  -- use server-side image map --
  >

<!-- USEMAP points to a MAP element which may be in this document
  or an external document, although the latter is not widely supported -->

<!--==================== OBJECT ======================================-->
<!--
  OBJECT is used to embed objects as part of HTML pages
  PARAM elements should precede other content. SGML mixed content
  model technicality precludes specifying this formally ...
-->

<!ELEMENT OBJECT - - (PARAM | %flow;)*
 -- generic embedded object -->
<!ATTLIST OBJECT
  %attrs;                              -- %coreattrs, %i18n, %events --
  declare     (declare)      #IMPLIED  -- declare but don't instantiate flag --
  classid     %URI;          #IMPLIED  -- identifies an implementation --
  codebase    %URI;          #IMPLIED  -- base URI for classid, data, archive--
  data        %URI;          #IMPLIED  -- reference to object's data --
  type        %ContentType;  #IMPLIED  -- content type for data --
  codetype    %ContentType;  #IMPLIED  -- content type for code --
  archive     %URI;          #IMPLIED  -- space separated archive list --
  standby     %Text;         #IMPLIED  -- message to show while loading --
  height      %Length;       #IMPLIED  -- override height --
  width       %Length;       #IMPLIED  -- override width --
  usemap      %URI;          #IMPLIED  -- use client-side image map --
  name        CDATA          #IMPLIED  -- submit as part of form --
  tabindex    NUMBER         #IMPLIED  -- position in tabbing order --
  %reserved;                           -- reserved for possible future use --
  >

<!ELEMENT PARAM - O EMPTY              -- named property value -->
<!ATTLIST PARAM
  id          ID             #IMPLIED  -- document-wide unique id --
  name        CDATA          #REQUIRED -- property name --
  value       CDATA          #IMPLIED  -- property value --
  valuetype   (DATA|REF|OBJECT) DATA   -- How to interpret value --
  type        %ContentType;  #IMPLIED  -- content type for value
                                          when valuetype=ref --
  >

<!--=================== Horizontal Rule ==================================-->

<!ELEMENT HR - O EMPTY -- horizontal rule -->
<!ATTLIST HR
  %coreattrs;                          -- id, class, style, title --
  %events;
  >

<!--=================== Paragraphs =======================================-->

<!ELEMENT P - O (%inline;)*            -- paragraph -->
<!ATTLIST P
  %attrs;                              -- %coreattrs, %i18n, %events --
  >

<!--=================== Headings =========================================-->

<!--
  There are six levels of headings from H1 (the most important)
  to H6 (the least important).
-->

<!ELEMENT (%heading;)  - - (%inline;)* -- heading -->
<!ATTLIST (%heading;)
  %attrs;                              -- %coreattrs, %i18n, %events --
  >

<!--=================== Preformatted Text ================================-->

<!-- excludes markup for images and changes in font size -->
<!ENTITY % pre.exclusion "IMG|OBJECT|BIG|SMALL|SUB|SUP">

<!ELEMENT PRE - - (%inline;)* -(%pre.exclusion;) -- preformatted text -->
<!ATTLIST PRE
  %attrs;                              -- %coreattrs, %i18n, %events --
  >

<!--===================== Inline Quotes ==================================-->

<!ELEMENT Q - - (%inline;)*            -- short inline quotation -->
<!ATTLIST Q
  %attrs;                              -- %coreattrs, %i18n, %events --
  cite        %URI;          #IMPLIED  -- URI for source document or msg --
  >

<!--=================== Block-like Quotes ================================-->

<!ELEMENT BLOCKQUOTE - - (%block;|SCRIPT)+ -- long quotation -->
<!ATTLIST BLOCKQUOTE
  %attrs;                              -- %coreattrs, %i18n, %events --
  cite        %URI;          #IMPLIED  -- URI for source document or msg --
  >

<!--=================== Inserted/Deleted Text ============================-->

<!-- INS/DEL are handled by inclusion on BODY -->
<!ELEMENT (INS|DEL) - - (%flow;)*      -- inserted text, deleted text -->
<!ATTLIST (INS|DEL)
  %attrs;                              -- %coreattrs, %i18n, %events --
  cite        %URI;          #IMPLIED  -- info on reason for change --
  datetime    %Datetime;     #IMPLIED  -- date and time of change --
  >

<!--=================== Lists ============================================-->

<!-- definition lists - DT for term, DD for its definition -->

<!ELEMENT DL - - (DT|DD)+              -- definition list -->
<!ATTLIST DL
  %attrs;                              -- %coreattrs, %i18n, %events --
  >

<!ELEMENT DT - O (%inline;)*           -- definition term -->
<!ELEMENT DD - O (%flow;)*             -- definition description -->
<!ATTLIST (DT|DD)
  %attrs;                              -- %coreattrs, %i18n, %events --
  >

<!ELEMENT OL - - (LI)+                 -- ordered list -->
<!ATTLIST OL
  %attrs;                              -- %coreattrs, %i18n, %events --
  >

<!-- Unordered Lists (UL) bullet styles -->
<!ELEMENT UL - - (LI)+                 -- unordered list -->
<!ATTLIST UL
  %attrs;                              -- %coreattrs, %i18n, %events --
  >

<!ELEMENT LI - O (%flow;)*             -- list item -->
<!ATTLIST LI
  %attrs;                              -- %coreattrs, %i18n, %events --
  >

<!--================ Forms ===============================================-->
<!ELEMENT FORM - - (%block;|SCRIPT)+ -(FORM) -- interactive form -->
<!ATTLIST FORM
  %attrs;                              -- %coreattrs, %i18n, %events --
  action      %URI;          #REQUIRED -- server-side form handler --
  method      (GET|POST)     GET       -- HTTP method used to submit the form--
  enctype     %ContentType;  "application/x-www-form-urlencoded"
  onsubmit    %Script;       #IMPLIED  -- the form was submitted --
  onreset     %Script;       #IMPLIED  -- the form was reset --
  accept-charset %Charsets;  #IMPLIED  -- list of supported charsets --
  >

<!-- Each label must not contain more than ONE field -->
<!ELEMENT LABEL - - (%inline;)* -(LABEL) -- form field label text -->
<!ATTLIST LABEL
  %attrs;                              -- %coreattrs, %i18n, %events --
  for         IDREF          #IMPLIED  -- matches field ID value --
  accesskey   %Character;    #IMPLIED  -- accessibility key character --
  onfocus     %Script;       #IMPLIED  -- the element got the focus --
  onblur      %Script;       #IMPLIED  -- the element lost the focus --
  >

<!ENTITY % InputType
  "(TEXT | PASSWORD | CHECKBOX |
    RADIO | SUBMIT | RESET |
    FILE | HIDDEN | IMAGE | BUTTON)"
   >

<!-- attribute name required for all but submit & reset -->
<!ELEMENT INPUT - O EMPTY              -- form control -->
<!ATTLIST INPUT
  %attrs;                              -- %coreattrs, %i18n, %events --
  type        %InputType;    TEXT      -- what kind of widget is needed --
  name        CDATA          #IMPLIED  -- submit as part of form --
  value       CDATA          #IMPLIED  -- required for radio and checkboxes --
  checked     (checked)      #IMPLIED  -- for radio buttons and check boxes --
  disabled    (disabled)     #IMPLIED  -- unavailable in this context --
  readonly    (readonly)     #IMPLIED  -- for text and passwd --
  size        CDATA          #IMPLIED  -- specific to each type of field --
  maxlength   NUMBER         #IMPLIED  -- max chars for text fields --
  src         %URI;          #IMPLIED  -- for fields with images --
  alt         CDATA          #IMPLIED  -- short description --
  usemap      %URI;          #IMPLIED  -- use client-side image map --
  tabindex    NUMBER         #IMPLIED  -- position in tabbing order --
  accesskey   %Character;    #IMPLIED  -- accessibility key character --
  onfocus     %Script;       #IMPLIED  -- the element got the focus --
  onblur      %Script;       #IMPLIED  -- the element lost the focus --
  onselect    %Script;       #IMPLIED  -- some text was selected --
  onchange    %Script;       #IMPLIED  -- the element value was changed --
  accept      %ContentTypes; #IMPLIED  -- list of MIME types for file upload --
  %reserved;                           -- reserved for possible future use --
  >

<!ELEMENT SELECT - - (OPTGROUP|OPTION)+ -- option selector -->
<!ATTLIST SELECT
  %attrs;                              -- %coreattrs, %i18n, %events --
  name        CDATA          #IMPLIED  -- field name --
  size        NUMBER         #IMPLIED  -- rows visible --
  multiple    (multiple)     #IMPLIED  -- default is single selection --
  disabled    (disabled)     #IMPLIED  -- unavailable in this context --
  tabindex    NUMBER         #IMPLIED  -- position in tabbing order --
  onfocus     %Script;       #IMPLIED  -- the element got the focus --
  onblur      %Script;       #IMPLIED  -- the element lost the focus --
  onchange    %Script;       #IMPLIED  -- the element value was changed --
  %reserved;                           -- reserved for possible future use --
  >

<!ELEMENT OPTGROUP - - (OPTION)+ -- option group -->
<!ATTLIST OPTGROUP
  %attrs;                              -- %coreattrs, %i18n, %events --
  disabled    (disabled)     #IMPLIED  -- unavailable in this context --
  label       %Text;         #REQUIRED -- for use in hierarchical menus --
  >

<!ELEMENT OPTION - O (#PCDATA)         -- selectable choice -->
<!ATTLIST OPTION
  %attrs;                              -- %coreattrs, %i18n, %events --
  selected    (selected)     #IMPLIED
  disabled    (disabled)     #IMPLIED  -- unavailable in this context --
  label       %Text;         #IMPLIED  -- for use in hierarchical menus --
  value       CDATA          #IMPLIED  -- defaults to element content --
  >

<!ELEMENT TEXTAREA - - (#PCDATA)       -- multi-line text field -->
<!ATTLIST TEXTAREA
  %attrs;                              -- %coreattrs, %i18n, %events --
  name        CDATA          #IMPLIED
  rows        NUMBER         #REQUIRED
  cols        NUMBER         #REQUIRED
  disabled    (disabled)     #IMPLIED  -- unavailable in this context --
  readonly    (readonly)     #IMPLIED
  tabindex    NUMBER         #IMPLIED  -- position in tabbing order --
  accesskey   %Character;    #IMPLIED  -- accessibility key character --
  onfocus     %Script;       #IMPLIED  -- the element got the focus --
  onblur      %Script;       #IMPLIED  -- the element lost the focus --
  onselect    %Script;       #IMPLIED  -- some text was selected --
  onchange    %Script;       #IMPLIED  -- the element value was changed --
  %reserved;                           -- reserved for possible future use --
  >

<!--
  #PCDATA is to solve the mixed content problem,
  per specification only whitespace is allowed there!
 -->
<!ELEMENT FIELDSET - - (#PCDATA,LEGEND,(%flow;)*) -- form control group -->
<!ATTLIST FIELDSET
  %attrs;                              -- %coreattrs, %i18n, %events --
  >

<!ELEMENT LEGEND - - (%inline;)*       -- fieldset legend -->
<!ENTITY % LAlign "(top|bottom|left|right)">

<!ATTLIST LEGEND
  %attrs;                              -- %coreattrs, %i18n, %events --
  accesskey   %Character;    #IMPLIED  -- accessibility key character --
  >

<!ELEMENT BUTTON - -
     (%flow;)* -(A|%formctrl;|FORM|FIELDSET)
     -- push button -->
<!ATTLIST BUTTON
  %attrs;                              -- %coreattrs, %i18n, %events --
  name        CDATA          #IMPLIED
  value       CDATA          #IMPLIED  -- sent to server when submitted --
  type        (button|submit|reset) submit -- for use as form button --
  disabled    (disabled)     #IMPLIED  -- unavailable in this context --
  tabindex    NUMBER         #IMPLIED  -- position in tabbing order --
  accesskey   %Character;    #IMPLIED  -- accessibility key character --
  onfocus     %Script;       #IMPLIED  -- the element got the focus --
  onblur      %Script;       #IMPLIED  -- the element lost the focus --
  %reserved;                           -- reserved for possible future use --
  >

<!--======================= Tables =======================================-->

<!-- IETF HTML table standard, see [RFC1942] -->

<!--
 The BORDER attribute sets the thickness of the frame around the
 table. The default units are screen pixels.

 The FRAME attribute specifies which parts of the frame around
 the table should be rendered. The values are not the same as
 CALS to avoid a name clash with the VALIGN attribute.

 The value "border" is included for backwards compatibility with
 <TABLE BORDER> which yields frame=border and border=implied
 For <TABLE BORDER=1> you get border=1 and frame=implied. In this
 case, it is appropriate to treat this as frame=border for backwards
 compatibility with deployed browsers.
-->
<!ENTITY % TFrame "(void|above|below|hsides|lhs|rhs|vsides|box|border)">

<!--
 The RULES attribute defines which rules to draw between cells:

 If RULES is absent then assume:
     "none" if BORDER is absent or BORDER=0 otherwise "all"
-->

<!ENTITY % TRules "(none | groups | rows | cols | all)">

<!-- horizontal placement of table relative to document -->
<!ENTITY % TAlign "(left|center|right)">

<!-- horizontal alignment attributes for cell contents -->
<!ENTITY % cellhalign
  "align      (left|center|right|justify|char) #IMPLIED
   char       %Character;    #IMPLIED  -- alignment char, e.g. char=':' --
   charoff    %Length;       #IMPLIED  -- offset for alignment char --"
  >

<!-- vertical alignment attributes for cell contents -->
<!ENTITY % cellvalign
  "valign     (top|middle|bottom|baseline) #IMPLIED"
  >

<!ELEMENT TABLE - -
     (CAPTION?, (COL*|COLGROUP*), THEAD?, TFOOT?, TBODY+)>
<!ELEMENT CAPTION  - - (%inline;)*     -- table caption -->
<!ELEMENT THEAD    - O (TR)+           -- table header -->
<!ELEMENT TFOOT    - O (TR)+           -- table footer -->
<!ELEMENT TBODY    O O (TR)+           -- table body -->
<!ELEMENT COLGROUP - O (col)*          -- table column group -->
<!ELEMENT COL      - O EMPTY           -- table column -->
<!ELEMENT TR       - O (TH|TD)+        -- table row -->
<!ELEMENT (TH|TD)  - O (%flow;)*       -- table header cell, table data cell-->

<!ATTLIST TABLE                        -- table element --
  %attrs;                              -- %coreattrs, %i18n, %events --
  summary     %Text;         #IMPLIED  -- purpose/structure for speech output--
  width       %Length;       #IMPLIED  -- table width --
  border      %Pixels;       #IMPLIED  -- controls frame width around table --
  frame       %TFrame;       #IMPLIED  -- which parts of frame to render --
  rules       %TRules;       #IMPLIED  -- rulings between rows and cols --
  cellspacing %Length;       #IMPLIED  -- spacing between cells --
  cellpadding %Length;       #IMPLIED  -- spacing within cells --
  %reserved;                           -- reserved for possible future use --
  datapagesize CDATA         #IMPLIED  -- reserved for possible future use --
  >

<!ENTITY % CAlign "(top|bottom|left|right)">

<!ATTLIST CAPTION
  %attrs;                              -- %coreattrs, %i18n, %events --
  >

<!--
COLGROUP groups a set of COL elements. It allows you to group
several semantically related columns together.
-->
<!ATTLIST COLGROUP
  %attrs;                              -- %coreattrs, %i18n, %events --
  span        NUMBER         1         -- default number of columns in group --
  width       %MultiLength;  #IMPLIED  -- default width for enclosed COLs --
  %cellhalign;                         -- horizontal alignment in cells --
  %cellvalign;                         -- vertical alignment in cells --
  >

<!--
 COL elements define the alignment properties for cells in
 one or more columns.

 The WIDTH attribute specifies the width of the columns, e.g.

     width=64        width in screen pixels
     width=0.5*      relative width of 0.5

 The SPAN attribute causes the attributes of one
 COL element to apply to more than one column.
-->
<!ATTLIST COL                          -- column groups and properties --
  %attrs;                              -- %coreattrs, %i18n, %events --
  span        NUMBER         1         -- COL attributes affect N columns --
  width       %MultiLength;  #IMPLIED  -- column width specification --
  %cellhalign;                         -- horizontal alignment in cells --
  %cellvalign;                         -- vertical alignment in cells --
  >

<!--
    Use THEAD to duplicate headers when breaking table
    across page boundaries, or for static headers when
    TBODY sections are rendered in scrolling panel.

    Use TFOOT to duplicate footers when breaking table
    across page boundaries, or for static footers when
    TBODY sections are rendered in scrolling panel.

    Use multiple TBODY sections when rules are needed
    between groups of table rows.
-->
<!ATTLIST (THEAD|TBODY|TFOOT)          -- table section --
  %attrs;                              -- %coreattrs, %i18n, %events --
  %cellhalign;                         -- horizontal alignment in cells --
  %cellvalign;                         -- vertical alignment in cells --
  >

<!ATTLIST TR                           -- table row --
  %attrs;                              -- %coreattrs, %i18n, %events --
  %cellhalign;                         -- horizontal alignment in cells --
  %cellvalign;                         -- vertical alignment in cells --
  >

<!-- Scope is simpler than axes attribute for common tables -->
<!ENTITY % Scope "(row|col|rowgroup|colgroup)">

<!-- TH is for headers, TD for data, but for cells acting as both use TD -->
<!ATTLIST (TH|TD)                      -- header or data cell --
  %attrs;                              -- %coreattrs, %i18n, %events --
  abbr        %Text;         #IMPLIED  -- abbreviation for header cell --
  axis        CDATA          #IMPLIED  -- names groups of related headers--
  headers     IDREFS         #IMPLIED  -- list of id's for header cells --
  scope       %Scope;        #IMPLIED  -- scope covered by header cells --
  rowspan     NUMBER         1         -- number of rows spanned by cell --
  colspan     NUMBER         1         -- number of cols spanned by cell --
  %cellhalign;                         -- horizontal alignment in cells --
  %cellvalign;                         -- vertical alignment in cells --
  >

<!--================ Document Head =======================================-->
<!-- %head.misc; defined earlier on as "SCRIPT|STYLE|META|LINK|OBJECT" -->
<!ENTITY % head.content "TITLE & BASE?">

<!ELEMENT HEAD O O (%head.content;) +(%head.misc;) -- document head -->
<!ATTLIST HEAD
  %i18n;                               -- lang, dir --
  profile     %URI;          #IMPLIED  -- named dictionary of meta info --
  >

<!-- The TITLE element is not considered part of the flow of text.
       It should be displayed, for example as the page header or
       window title. Exactly one title is required per document.
    -->
<!ELEMENT TITLE - - (#PCDATA) -(%head.misc;) -- document title -->
<!ATTLIST TITLE %i18n>

<!ELEMENT BASE - O EMPTY               -- document base URI -->
<!ATTLIST BASE
  href        %URI;          #REQUIRED -- URI that acts as base URI --
  >

<!ELEMENT META - O EMPTY               -- generic metainformation -->
<!ATTLIST META
  %i18n;                               -- lang, dir, for use with content --
  http-equiv  NAME           #IMPLIED  -- HTTP response header name  --
  name        NAME           #IMPLIED  -- metainformation name --
  content     CDATA          #REQUIRED -- associated information --
  scheme      CDATA          #IMPLIED  -- select form of content --
  >

<!ELEMENT STYLE - - %StyleSheet        -- style info -->
<!ATTLIST STYLE
  %i18n;                               -- lang, dir, for use with title --
  type        %ContentType;  #REQUIRED -- content type of style language --
  media       %MediaDesc;    #IMPLIED  -- designed for use with these media --
  title       %Text;         #IMPLIED  -- advisory title --
  >

<!ELEMENT SCRIPT - - %Script;          -- script statements -->
<!ATTLIST SCRIPT
  charset     %Charset;      #IMPLIED  -- char encoding of linked resource --
  type        %ContentType;  #REQUIRED -- content type of script language --
  language    CDATA          #IMPLIED  -- predefined script language name --
  src         %URI;          #IMPLIED  -- URI for an external script --
  defer       (defer)        #IMPLIED  -- UA may defer execution of script --
  event       CDATA          #IMPLIED  -- reserved for possible future use --
  for         %URI;          #IMPLIED  -- reserved for possible future use --
  >

<!ELEMENT NOSCRIPT - - (%block;)+
  -- alternate content container for non script-based rendering -->
<!ATTLIST NOSCRIPT
  %attrs;                              -- %coreattrs, %i18n, %events --
  >

<!--================ Document Structure ==================================-->
<!ENTITY % html.content "HEAD, BODY">

<!ELEMENT HTML O O (%html.content;)    -- document root element -->
<!ATTLIST HTML
  %i18n;                               -- lang, dir --
  >

                  22 Transitional Document Type Definition

<!--
    This is the HTML 4.0 Transitional DTD, which includes
    presentation attributes and elements that W3C expects to phase out
    as support for style sheets matures. Authors should use the Strict
    DTD when possible, but may use the Transitional DTD when support
    for presentation attribute and elements is required.

    HTML 4.0 includes mechanisms for style sheets, scripting,
    embedding objects, improved support for right to left and mixed
    direction text, and enhancements to forms for improved
    accessibility for people with disabilities.

          Draft: $Date: 1997/12/18 09:36:02 $

          Authors:
              Dave Raggett <dsr@w3.org>
              Arnaud Le Hors <lehors@w3.org>
              Ian Jacobs <ij@w3.org>

    Further information about HTML 4.0 is available at:

        http://www.w3.org/TR/REC-html40
-->
<!ENTITY % HTML.Version "-//W3C//DTD HTML 4.0 Transitional//EN"
  -- Typical usage:

    <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"
            "http://www.w3.org/TR/REC-html40/loose.dtd">
    <html>
    <head>
    ...
    </head>
    <body>
    ...
    </body>
    </html>

    The URI used as a system identifier with the public identifier allows
    the user agent to download the DTD and entity sets as needed.

    The FPI for the Strict HTML 4.0 DTD is:

        "-//W3C//DTD HTML 4.0//EN"

    and its URI is:

        http://www.w3.org/TR/REC-html40/strict.dtd

    Authors should use the Strict DTD unless they need the
    presentation control for user agents that don't (adequately)
    support style sheets.

    If you are writing a document that includes frames, use
    the following FPI:

        "-//W3C//DTD HTML 4.0 Frameset//EN"

    with the URI:

        http://www.w3.org/TR/REC-html40/frameset.dtd

    The following URIs are supported in relation to HTML 4.0

    "http://www.w3.org/TR/REC-html40/strict.dtd" (Strict DTD)
    "http://www.w3.org/TR/REC-html40/loose.dtd" (Loose DTD)
    "http://www.w3.org/TR/REC-html40/frameset.dtd" (Frameset DTD)
    "http://www.w3.org/TR/REC-html40/HTMLlat1.ent" (Latin-1 entities)
    "http://www.w3.org/TR/REC-html40/HTMLsymbol.ent" (Symbol entities)
    "http://www.w3.org/TR/REC-html40/HTMLspecial.ent" (Special entities)

    These URIs point to the latest version of each file. To reference
    this specific revision use the following URIs:

    "http://www.w3.org/TR/REC-html40-971218/strict.dtd"
    "http://www.w3.org/TR/REC-html40-971218/loose.dtd"
    "http://www.w3.org/TR/REC-html40-971218/frameset.dtd"
    "http://www.w3.org/TR/REC-html40-971218/HTMLlat1.ent"
    "http://www.w3.org/TR/REC-html40-971218/HTMLsymbol.ent"
    "http://www.w3.org/TR/REC-html40-971218/HTMLspecial.ent"

-->

<!--================== Imported Names ====================================-->

<!ENTITY % ContentType "CDATA"
    -- media type, as per [RFC2045]
    -->

<!ENTITY % ContentTypes "CDATA"
    -- comma-separated list of media types, as per [RFC2045]
    -->

<!ENTITY % Charset "CDATA"
    -- a character encoding, as per [RFC2045]
    -->

<!ENTITY % Charsets "CDATA"
    -- a space separated list of character encodings, as per [RFC2045]
    -->

<!ENTITY % LanguageCode "NAME"
    -- a language code, as per [RFC1766]
    -->

<!ENTITY % Character "CDATA"
    -- a single character from [ISO10646]
    -->

<!ENTITY % LinkTypes "CDATA"
    -- space-separated list of link types
    -->

<!ENTITY % MediaDesc "CDATA"
    -- single or comma-separated list of media descriptors
    -->

<!ENTITY % URI "CDATA"
    -- a Uniform Resource Identifier,
       see [URI]
    -->

<!ENTITY % Datetime "CDATA" -- date and time information. ISO date format -->

<!ENTITY % Script "CDATA" -- script expression -->

<!ENTITY % StyleSheet "CDATA" -- style sheet data -->

<!ENTITY % FrameTarget "CDATA" -- render in this frame -->

<!ENTITY % Text "CDATA">

<!-- Parameter Entities -->

<!ENTITY % head.misc "SCRIPT|STYLE|META|LINK|OBJECT" -- repeatable head elements -->

<!ENTITY % heading "H1|H2|H3|H4|H5|H6">

<!ENTITY % list "UL | OL |  DIR | MENU">

<!ENTITY % preformatted "PRE">

<!ENTITY % Color "CDATA" -- a color using sRGB: #RRGGBB as Hex values -->

<!-- There are also 16 widely known color names with their sRGB values:

    Black  = #000000    Green  = #008000
    Silver = #C0C0C0    Lime   = #00FF00
    Gray   = #808080    Olive  = #808000
    White  = #FFFFFF    Yellow = #FFFF00
    Maroon = #800000    Navy   = #000080
    Red    = #FF0000    Blue   = #0000FF
    Purple = #800080    Teal   = #008080
    Fuchsia= #FF00FF    Aqua   = #00FFFF
 -->

<!ENTITY % bodycolors "
  bgcolor     %Color;        #IMPLIED  -- document background color --
  text        %Color;        #IMPLIED  -- document text color --
  link        %Color;        #IMPLIED  -- color of links --
  vlink       %Color;        #IMPLIED  -- color of visited links --
  alink       %Color;        #IMPLIED  -- color of selected links --
  ">

<!--================ Character mnemonic entities =========================-->

<!ENTITY % HTMLlat1 PUBLIC
   "-//W3C//ENTITIES Latin1//EN//HTML"
   "http://www.w3.org/TR/REC-html40-971218/HTMLlat1.ent">
%HTMLlat1;

<!ENTITY % HTMLsymbol PUBLIC
   "-//W3C//ENTITIES Symbols//EN//HTML"
   "http://www.w3.org/TR/REC-html40-971218/HTMLsymbol.ent">
%HTMLsymbol;

<!ENTITY % HTMLspecial PUBLIC
   "-//W3C//ENTITIES Special//EN//HTML"
   "http://www.w3.org/TR/REC-html40-971218/HTMLspecial.ent">
%HTMLspecial;
<!--=================== Generic Attributes ===============================-->

<!ENTITY % coreattrs
 "id          ID             #IMPLIED  -- document-wide unique id --
  class       CDATA          #IMPLIED  -- space separated list of classes --
  style       %StyleSheet;   #IMPLIED  -- associated style info --
  title       %Text;         #IMPLIED  -- advisory title/amplification --"
  >

<!ENTITY % i18n
 "lang        %LanguageCode; #IMPLIED  -- language code --
  dir         (ltr|rtl)      #IMPLIED  -- direction for weak/neutral text --"
  >

<!ENTITY % events
 "onclick     %Script;       #IMPLIED  -- a pointer button was clicked --
  ondblclick  %Script;       #IMPLIED  -- a pointer button was double clicked--
  onmousedown %Script;       #IMPLIED  -- a pointer button was pressed down --
  onmouseup   %Script;       #IMPLIED  -- a pointer button was released --
  onmouseover %Script;       #IMPLIED  -- a pointer was moved onto --
  onmousemove %Script;       #IMPLIED  -- a pointer was moved within --
  onmouseout  %Script;       #IMPLIED  -- a pointer was moved away --
  onkeypress  %Script;       #IMPLIED  -- a key was pressed and released --
  onkeydown   %Script;       #IMPLIED  -- a key was pressed down --
  onkeyup     %Script;       #IMPLIED  -- a key was released --"
  >

<!-- Reserved Feature Switch -->
<!ENTITY % HTML.Reserved "IGNORE">

<!-- The following attributes are reserved for possible future use -->
<![ %HTML.Reserved; [
<!ENTITY % reserved
 "datasrc     %URI;          #IMPLIED  -- a single or tabular Data Source --
  datafld     CDATA          #IMPLIED  -- the property or column name --
  dataformatas (plaintext|html) plaintext -- text or html --"
  >
]]>

<!ENTITY % reserved "">

<!ENTITY % attrs "%coreattrs; %i18n; %events;">

<!ENTITY % align "align (left|center|right|justify)  #IMPLIED"
                   -- default is left for ltr paragraphs, right for rtl --
  >

<!--=================== Text Markup ======================================-->

<!ENTITY % fontstyle
 "TT | I | B | U | S | STRIKE | BIG | SMALL">

<!ENTITY % phrase "EM | STRONG | DFN | CODE |
                   SAMP | KBD | VAR | CITE | ABBR | ACRONYM" >

<!ENTITY % special
   "A | IMG | APPLET | OBJECT | FONT | BASEFONT | BR | SCRIPT |
    MAP | Q | SUB | SUP | SPAN | BDO | IFRAME">

<!ENTITY % formctrl "INPUT | SELECT | TEXTAREA | LABEL | BUTTON">

<!-- %inline; covers inline or "text-level" elements -->
<!ENTITY % inline "#PCDATA | %fontstyle; | %phrase; | %special; | %formctrl;">

<!ELEMENT (%fontstyle;|%phrase;) - - (%inline;)*>
<!ATTLIST (%fontstyle;|%phrase;)
  %attrs;                              -- %coreattrs, %i18n, %events --
  >

<!ELEMENT (SUB|SUP) - - (%inline;)*    -- subscript, superscript -->
<!ATTLIST (SUB|SUP)
  %attrs;                              -- %coreattrs, %i18n, %events --
  >

<!ELEMENT SPAN - - (%inline;)*         -- generic language/style container -->
<!ATTLIST SPAN
  %attrs;                              -- %coreattrs, %i18n, %events --
  %reserved;                           -- reserved for possible future use --
  >

<!ELEMENT BDO - - (%inline;)*          -- I18N BiDi over-ride -->
<!ATTLIST BDO
  %coreattrs;                          -- id, class, style, title --
  lang        %LanguageCode; #IMPLIED  -- language code --
  dir         (ltr|rtl)      #REQUIRED -- directionality --
  >

<!ELEMENT BASEFONT - O EMPTY           -- base font size -->
<!ATTLIST BASEFONT
  id          ID             #IMPLIED  -- document-wide unique id --
  size        CDATA          #REQUIRED -- base font size for FONT elements --
  color       %Color;        #IMPLIED  -- text color --
  face        CDATA          #IMPLIED  -- comma separated list of font names --
  >

<!ELEMENT FONT - - (%inline;)*         -- local change to font -->
<!ATTLIST FONT
  %coreattrs;                          -- id, class, style, title --
  %i18n;                               -- lang, dir --
  size        CDATA          #IMPLIED  -- [+|-]nn e.g. size="+1", size="4" --
  color       %Color;        #IMPLIED  -- text color --
  face        CDATA          #IMPLIED  -- comma separated list of font names --
  >

<!ELEMENT BR - O EMPTY                 -- forced line break -->
<!ATTLIST BR
  %coreattrs;                          -- id, class, style, title --
  clear       (left|all|right|none) none -- control of text flow --
  >

<!--================== HTML content models ===============================-->

<!--
    HTML has two basic content models:

        %inline;     character level elements and text strings
        %block;      block-like elements e.g. paragraphs and lists
-->

<!ENTITY % block
     "P | %heading; | %list; | %preformatted; | DL | DIV | CENTER |
      NOSCRIPT | NOFRAMES | BLOCKQUOTE | FORM | ISINDEX | HR |
      TABLE | FIELDSET | ADDRESS">

<!ENTITY % flow "%block; | %inline;">

<!--=================== Document Body ====================================-->

<!ELEMENT BODY O O (%flow;)* +(INS|DEL) -- document body -->
<!ATTLIST BODY
  %attrs;                              -- %coreattrs, %i18n, %events --
  onload          %Script;   #IMPLIED  -- the document has been loaded --
  onunload        %Script;   #IMPLIED  -- the document has been removed --
  background      %URI;      #IMPLIED  -- texture tile for document
                                          background --
  %bodycolors;                         -- bgcolor, text, link, vlink, alink --
  >

<!ELEMENT ADDRESS - - ((%inline;)|P)*  -- information on author -->
<!ATTLIST ADDRESS
  %attrs;                              -- %coreattrs, %i18n, %events --
  >

<!ELEMENT DIV - - (%flow;)*            -- generic language/style container -->
<!ATTLIST DIV
  %attrs;                              -- %coreattrs, %i18n, %events --
  %align;                              -- align, text alignment --
  %reserved;                           -- reserved for possible future use --
  >

<!ELEMENT CENTER - - (%flow;)*         -- shorthand for DIV align=center -->
<!ATTLIST CENTER
  %attrs;                              -- %coreattrs, %i18n, %events --
  >

<!--================== The Anchor Element ================================-->

<!ENTITY % Shape "(rect|circle|poly|default)">
<!ENTITY % Coords "CDATA" -- comma separated list of lengths -->

<!ELEMENT A - - (%inline;)* -(A)       -- anchor -->
<!ATTLIST A
  %attrs;                              -- %coreattrs, %i18n, %events --
  charset     %Charset;      #IMPLIED  -- char encoding of linked resource --
  type        %ContentType;  #IMPLIED  -- advisory content type --
  name        CDATA          #IMPLIED  -- named link end --
  href        %URI;          #IMPLIED  -- URI for linked resource --
  hreflang    %LanguageCode; #IMPLIED  -- language code --
  target      %FrameTarget;  #IMPLIED  -- render in this frame --
  rel         %LinkTypes;    #IMPLIED  -- forward link types --
  rev         %LinkTypes;    #IMPLIED  -- reverse link types --
  accesskey   %Character;    #IMPLIED  -- accessibility key character --
  shape       %Shape;        rect      -- for use with client-side image maps --
  coords      %Coords;       #IMPLIED  -- for use with client-side image maps --
  tabindex    NUMBER         #IMPLIED  -- position in tabbing order --
  onfocus     %Script;       #IMPLIED  -- the element got the focus --
  onblur      %Script;       #IMPLIED  -- the element lost the focus --
  >

<!--================== Client-side image maps ============================-->

<!-- These can be placed in the same document or grouped in a
     separate document although this isn't yet widely supported -->

<!ELEMENT MAP - - ((%block;)+ | AREA+) -- client-side image map -->
<!ATTLIST MAP
  %attrs;                              -- %coreattrs, %i18n, %events --
  name        CDATA          #REQUIRED -- for reference by usemap --
  >

<!ELEMENT AREA - O EMPTY               -- client-side image map area -->
<!ATTLIST AREA
  %attrs;                              -- %coreattrs, %i18n, %events --
  shape       %Shape;        rect      -- controls interpretation of coords --
  coords      %Coords;       #IMPLIED  -- comma separated list of lengths --
  href        %URI;          #IMPLIED  -- URI for linked resource --
  target      %FrameTarget;  #IMPLIED  -- render in this frame --
  nohref      (nohref)       #IMPLIED  -- this region has no action --
  alt         %Text;         #REQUIRED -- short description --
  tabindex    NUMBER         #IMPLIED  -- position in tabbing order --
  accesskey   %Character;    #IMPLIED  -- accessibility key character --
  onfocus     %Script;       #IMPLIED  -- the element got the focus --
  onblur      %Script;       #IMPLIED  -- the element lost the focus --
  >

<!--================== The LINK Element ==================================-->

<!--
  Relationship values can be used in principle:

   a) for document specific toolbars/menus when used
      with the LINK element in document head e.g.
        start, contents, previous, next, index, end, help
   b) to link to a separate style sheet (rel=stylesheet)
   c) to make a link to a script (rel=script)
   d) by stylesheets to control how collections of
      html nodes are rendered into printed documents
   e) to make a link to a printable version of this document
      e.g. a postscript or pdf version (rel=alternate media=print)
-->

<!ELEMENT LINK - O EMPTY               -- a media-independent link -->
<!ATTLIST LINK
  %attrs;                              -- %coreattrs, %i18n, %events --
  charset     %Charset;      #IMPLIED  -- char encoding of linked resource --
  href        %URI;          #IMPLIED  -- URI for linked resource --
  hreflang    %LanguageCode; #IMPLIED  -- language code --
  type        %ContentType;  #IMPLIED  -- advisory content type --
  rel         %LinkTypes;    #IMPLIED  -- forward link types --
  rev         %LinkTypes;    #IMPLIED  -- reverse link types --
  media       %MediaDesc;    #IMPLIED  -- for rendering on these media --
  target      %FrameTarget;  #IMPLIED  -- render in this frame --
  >

<!--=================== Images ===========================================-->

<!-- Length defined in strict DTD for cellpadding/cellspacing -->
<!ENTITY % Length "CDATA" -- nn for pixels or nn% for percentage length -->
<!ENTITY % MultiLength "CDATA" -- pixel, percentage, or relative -->

<!ENTITY % MultiLengths "CDATA" -- comma-separated list of MultiLength -->

<!ENTITY % Pixels "CDATA" -- integer representing length in pixels -->

<!ENTITY % IAlign "(top|middle|bottom|left|right)" -- center? -->

<!-- To avoid problems with text-only UAs as well as
   to make image content understandable and navigable
   to users of non-visual UAs, you need to provide
   a description with ALT, and avoid server-side image maps -->
<!ELEMENT IMG - O EMPTY                -- Embedded image -->
<!ATTLIST IMG
  %attrs;                              -- %coreattrs, %i18n, %events --
  src         %URI;          #REQUIRED -- URI of image to embed --
  alt         %Text;         #REQUIRED -- short description --
  longdesc    %URI;          #IMPLIED  -- link to long description
                                          (complements alt) --
  height      %Length;       #IMPLIED  -- override height --
  width       %Length;       #IMPLIED  -- override width --
  usemap      %URI;          #IMPLIED  -- use client-side image map --
  ismap       (ismap)        #IMPLIED  -- use server-side image map --
  align       %IAlign;       #IMPLIED  -- vertical or horizontal alignment --
  border      %Length;       #IMPLIED  -- link border width --
  hspace      %Pixels;       #IMPLIED  -- horizontal gutter --
  vspace      %Pixels;       #IMPLIED  -- vertical gutter --
  >

<!-- USEMAP points to a MAP element which may be in this document
  or an external document, although the latter is not widely supported -->

<!--==================== OBJECT ======================================-->
<!--
  OBJECT is used to embed objects as part of HTML pages
  PARAM elements should precede other content. SGML mixed content
  model technicality precludes specifying this formally ...
-->

<!ELEMENT OBJECT - - (PARAM | %flow;)*
 -- generic embedded object -->
<!ATTLIST OBJECT
  %attrs;                              -- %coreattrs, %i18n, %events --
  declare     (declare)      #IMPLIED  -- declare but don't instantiate flag --
  classid     %URI;          #IMPLIED  -- identifies an implementation --
  codebase    %URI;          #IMPLIED  -- base URI for classid, data, archive--
  data        %URI;          #IMPLIED  -- reference to object's data --
  type        %ContentType;  #IMPLIED  -- content type for data --
  codetype    %ContentType;  #IMPLIED  -- content type for code --
  archive     %URI;          #IMPLIED  -- space separated archive list --
  standby     %Text;         #IMPLIED  -- message to show while loading --
  height      %Length;       #IMPLIED  -- override height --
  width       %Length;       #IMPLIED  -- override width --
  usemap      %URI;          #IMPLIED  -- use client-side image map --
  name        CDATA          #IMPLIED  -- submit as part of form --
  tabindex    NUMBER         #IMPLIED  -- position in tabbing order --
  align       %IAlign;       #IMPLIED  -- vertical or horizontal alignment --
  border      %Length;       #IMPLIED  -- link border width --
  hspace      %Pixels;       #IMPLIED  -- horizontal gutter --
  vspace      %Pixels;       #IMPLIED  -- vertical gutter --
  %reserved;                           -- reserved for possible future use --
  >

<!ELEMENT PARAM - O EMPTY              -- named property value -->
<!ATTLIST PARAM
  id          ID             #IMPLIED  -- document-wide unique id --
  name        CDATA          #REQUIRED -- property name --
  value       CDATA          #IMPLIED  -- property value --
  valuetype   (DATA|REF|OBJECT) DATA   -- How to interpret value --
  type        %ContentType;  #IMPLIED  -- content type for value
                                          when valuetype=ref --
  >

<!--=================== Java APPLET ==================================-->
<!--
  One of code or object attributes must be present.
  Place PARAM elements before other content.
-->
<!ELEMENT APPLET - - (PARAM | %flow;)* -- Java applet -->
<!ATTLIST APPLET
  %coreattrs;                          -- id, class, style, title --
  codebase    %URI;          #IMPLIED  -- optional base URI for applet --
  archive     CDATA          #IMPLIED  -- comma separated archive list --
  code        CDATA          #IMPLIED  -- applet class file --
  object      CDATA          #IMPLIED  -- serialized applet file --
  alt         %Text;         #IMPLIED  -- short description --
  name        CDATA          #IMPLIED  -- allows applets to find each other --
  width       %Length;       #REQUIRED -- initial width --
  height      %Length;       #REQUIRED -- initial height --
  align       %IAlign;       #IMPLIED  -- vertical or horizontal alignment --
  hspace      %Pixels;       #IMPLIED  -- horizontal gutter --
  vspace      %Pixels;       #IMPLIED  -- vertical gutter --
  >

<!--=================== Horizontal Rule ==================================-->

<!ELEMENT HR - O EMPTY -- horizontal rule -->
<!ATTLIST HR
  %coreattrs;                          -- id, class, style, title --
  %events;
  align       (left|center|right) #IMPLIED
  noshade     (noshade)      #IMPLIED
  size        %Pixels;       #IMPLIED
  width       %Length;       #IMPLIED
  >

<!--=================== Paragraphs =======================================-->

<!ELEMENT P - O (%inline;)*            -- paragraph -->
<!ATTLIST P
  %attrs;                              -- %coreattrs, %i18n, %events --
  %align;                              -- align, text alignment --
  >

<!--=================== Headings =========================================-->

<!--
  There are six levels of headings from H1 (the most important)
  to H6 (the least important).
-->

<!ELEMENT (%heading;)  - - (%inline;)* -- heading -->
<!ATTLIST (%heading;)
  %attrs;                              -- %coreattrs, %i18n, %events --
  %align;                              -- align, text alignment --
  >

<!--=================== Preformatted Text ================================-->

<!-- excludes markup for images and changes in font size -->
<!ENTITY % pre.exclusion "IMG|OBJECT|APPLET|BIG|SMALL|SUB|SUP|FONT|BASEFONT">

<!ELEMENT PRE - - (%inline;)* -(%pre.exclusion;) -- preformatted text -->
<!ATTLIST PRE
  %attrs;                              -- %coreattrs, %i18n, %events --
  width       NUMBER         #IMPLIED
  >

<!--===================== Inline Quotes ==================================-->

<!ELEMENT Q - - (%inline;)*            -- short inline quotation -->
<!ATTLIST Q
  %attrs;                              -- %coreattrs, %i18n, %events --
  cite        %URI;          #IMPLIED  -- URI for source document or msg --
  >

<!--=================== Block-like Quotes ================================-->

<!ELEMENT BLOCKQUOTE - - (%flow;)*     -- long quotation -->
<!ATTLIST BLOCKQUOTE
  %attrs;                              -- %coreattrs, %i18n, %events --
  cite        %URI;          #IMPLIED  -- URI for source document or msg --
  >

<!--=================== Inserted/Deleted Text ============================-->

<!-- INS/DEL are handled by inclusion on BODY -->
<!ELEMENT (INS|DEL) - - (%flow;)*      -- inserted text, deleted text -->
<!ATTLIST (INS|DEL)
  %attrs;                              -- %coreattrs, %i18n, %events --
  cite        %URI;          #IMPLIED  -- info on reason for change --
  datetime    %Datetime;     #IMPLIED  -- date and time of change --
  >

<!--=================== Lists ============================================-->

<!-- definition lists - DT for term, DD for its definition -->

<!ELEMENT DL - - (DT|DD)+              -- definition list -->
<!ATTLIST DL
  %attrs;                              -- %coreattrs, %i18n, %events --
  compact     (compact)      #IMPLIED  -- reduced interitem spacing --
  >

<!ELEMENT DT - O (%inline;)*           -- definition term -->
<!ELEMENT DD - O (%flow;)*             -- definition description -->
<!ATTLIST (DT|DD)
  %attrs;                              -- %coreattrs, %i18n, %events --
  >

<!-- Ordered lists (OL) Numbering style

    1   arablic numbers     1, 2, 3, ...
    a   lower alpha         a, b, c, ...
    A   upper alpha         A, B, C, ...
    i   lower roman         i, ii, iii, ...
    I   upper roman         I, II, III, ...

    The style is applied to the sequence number which by default
    is reset to 1 for the first list item in an ordered list.

    This can't be expressed directly in SGML due to case folding.
-->

<!ENTITY % OLStyle "CDATA"      -- constrained to: "(1|a|A|i|I)" -->

<!ELEMENT OL - - (LI)+                 -- ordered list -->
<!ATTLIST OL
  %attrs;                              -- %coreattrs, %i18n, %events --
  type        %OLStyle;      #IMPLIED  -- numbering style --
  compact     (compact)      #IMPLIED  -- reduced interitem spacing --
  start       NUMBER         #IMPLIED  -- starting sequence number --
  >

<!-- Unordered Lists (UL) bullet styles -->
<!ENTITY % ULStyle "(disc|square|circle)">

<!ELEMENT UL - - (LI)+                 -- unordered list -->
<!ATTLIST UL
  %attrs;                              -- %coreattrs, %i18n, %events --
  type        %ULStyle;      #IMPLIED  -- bullet style --
  compact     (compact)      #IMPLIED  -- reduced interitem spacing --
  >

<!ELEMENT (DIR|MENU) - - (LI)+ -(%block;) -- directory list, menu list -->
<!ATTLIST DIR
  %attrs;                              -- %coreattrs, %i18n, %events --
  compact     (compact)      #IMPLIED
  >
<!ATTLIST MENU
  %attrs;                              -- %coreattrs, %i18n, %events --
  compact     (compact)      #IMPLIED
  >

<!ENTITY % LIStyle "CDATA" -- constrained to: "(%ULStyle;|%OLStyle;)" -->

<!ELEMENT LI - O (%flow;)*             -- list item -->
<!ATTLIST LI
  %attrs;                              -- %coreattrs, %i18n, %events --
  type        %LIStyle;      #IMPLIED  -- list item style --
  value       NUMBER         #IMPLIED  -- reset sequence number --
  >

<!--================ Forms ===============================================-->
<!ELEMENT FORM - - (%flow;)* -(FORM)   -- interactive form -->
<!ATTLIST FORM
  %attrs;                              -- %coreattrs, %i18n, %events --
  action      %URI;          #REQUIRED -- server-side form handler --
  method      (GET|POST)     GET       -- HTTP method used to submit the form--
  enctype     %ContentType;  "application/x-www-form-urlencoded"
  onsubmit    %Script;       #IMPLIED  -- the form was submitted --
  onreset     %Script;       #IMPLIED  -- the form was reset --
  target      %FrameTarget;  #IMPLIED  -- render in this frame --
  accept-charset %Charsets;  #IMPLIED  -- list of supported charsets --
  >

<!-- Each label must not contain more than ONE field -->
<!ELEMENT LABEL - - (%inline;)* -(LABEL) -- form field label text -->
<!ATTLIST LABEL
  %attrs;                              -- %coreattrs, %i18n, %events --
  for         IDREF          #IMPLIED  -- matches field ID value --
  accesskey   %Character;    #IMPLIED  -- accessibility key character --
  onfocus     %Script;       #IMPLIED  -- the element got the focus --
  onblur      %Script;       #IMPLIED  -- the element lost the focus --
  >

<!ENTITY % InputType
  "(TEXT | PASSWORD | CHECKBOX |
    RADIO | SUBMIT | RESET |
    FILE | HIDDEN | IMAGE | BUTTON)"
   >

<!-- attribute name required for all but submit & reset -->
<!ELEMENT INPUT - O EMPTY              -- form control -->
<!ATTLIST INPUT
  %attrs;                              -- %coreattrs, %i18n, %events --
  type        %InputType;    TEXT      -- what kind of widget is needed --
  name        CDATA          #IMPLIED  -- submit as part of form --
  value       CDATA          #IMPLIED  -- required for radio and checkboxes --
  checked     (checked)      #IMPLIED  -- for radio buttons and check boxes --
  disabled    (disabled)     #IMPLIED  -- unavailable in this context --
  readonly    (readonly)     #IMPLIED  -- for text and passwd --
  size        CDATA          #IMPLIED  -- specific to each type of field --
  maxlength   NUMBER         #IMPLIED  -- max chars for text fields --
  src         %URI;          #IMPLIED  -- for fields with images --
  alt         CDATA          #IMPLIED  -- short description --
  usemap      %URI;          #IMPLIED  -- use client-side image map --
  tabindex    NUMBER         #IMPLIED  -- position in tabbing order --
  accesskey   %Character;    #IMPLIED  -- accessibility key character --
  onfocus     %Script;       #IMPLIED  -- the element got the focus --
  onblur      %Script;       #IMPLIED  -- the element lost the focus --
  onselect    %Script;       #IMPLIED  -- some text was selected --
  onchange    %Script;       #IMPLIED  -- the element value was changed --
  accept      %ContentTypes; #IMPLIED  -- list of MIME types for file upload --
  align       %IAlign;       #IMPLIED  -- vertical or horizontal alignment --
  %reserved;                           -- reserved for possible future use --
  >

<!ELEMENT SELECT - - (OPTGROUP|OPTION)+ -- option selector -->
<!ATTLIST SELECT
  %attrs;                              -- %coreattrs, %i18n, %events --
  name        CDATA          #IMPLIED  -- field name --
  size        NUMBER         #IMPLIED  -- rows visible --
  multiple    (multiple)     #IMPLIED  -- default is single selection --
  disabled    (disabled)     #IMPLIED  -- unavailable in this context --
  tabindex    NUMBER         #IMPLIED  -- position in tabbing order --
  onfocus     %Script;       #IMPLIED  -- the element got the focus --
  onblur      %Script;       #IMPLIED  -- the element lost the focus --
  onchange    %Script;       #IMPLIED  -- the element value was changed --
  %reserved;                           -- reserved for possible future use --
  >

<!ELEMENT OPTGROUP - - (OPTION)+ -- option group -->
<!ATTLIST OPTGROUP
  %attrs;                              -- %coreattrs, %i18n, %events --
  disabled    (disabled)     #IMPLIED  -- unavailable in this context --
  label       %Text;         #REQUIRED -- for use in hierarchical menus --
  >

<!ELEMENT OPTION - O (#PCDATA)         -- selectable choice -->
<!ATTLIST OPTION
  %attrs;                              -- %coreattrs, %i18n, %events --
  selected    (selected)     #IMPLIED
  disabled    (disabled)     #IMPLIED  -- unavailable in this context --
  label       %Text;         #IMPLIED  -- for use in hierarchical menus --
  value       CDATA          #IMPLIED  -- defaults to element content --
  >

<!ELEMENT TEXTAREA - - (#PCDATA)       -- multi-line text field -->
<!ATTLIST TEXTAREA
  %attrs;                              -- %coreattrs, %i18n, %events --
  name        CDATA          #IMPLIED
  rows        NUMBER         #REQUIRED
  cols        NUMBER         #REQUIRED
  disabled    (disabled)     #IMPLIED  -- unavailable in this context --
  readonly    (readonly)     #IMPLIED
  tabindex    NUMBER         #IMPLIED  -- position in tabbing order --
  accesskey   %Character;    #IMPLIED  -- accessibility key character --
  onfocus     %Script;       #IMPLIED  -- the element got the focus --
  onblur      %Script;       #IMPLIED  -- the element lost the focus --
  onselect    %Script;       #IMPLIED  -- some text was selected --
  onchange    %Script;       #IMPLIED  -- the element value was changed --
  %reserved;                           -- reserved for possible future use --
  >

<!--
  #PCDATA is to solve the mixed content problem,
  per specification only whitespace is allowed there!
 -->
<!ELEMENT FIELDSET - - (#PCDATA,LEGEND,(%flow;)*) -- form control group -->
<!ATTLIST FIELDSET
  %attrs;                              -- %coreattrs, %i18n, %events --
  >

<!ELEMENT LEGEND - - (%inline;)*       -- fieldset legend -->
<!ENTITY % LAlign "(top|bottom|left|right)">

<!ATTLIST LEGEND
  %attrs;                              -- %coreattrs, %i18n, %events --
  accesskey   %Character;    #IMPLIED  -- accessibility key character --
  align       %LAlign;       #IMPLIED  -- relative to fieldset --
  >

<!ELEMENT BUTTON - -
     (%flow;)* -(A|%formctrl;|FORM|ISINDEX|FIELDSET|IFRAME)
     -- push button -->
<!ATTLIST BUTTON
  %attrs;                              -- %coreattrs, %i18n, %events --
  name        CDATA          #IMPLIED
  value       CDATA          #IMPLIED  -- sent to server when submitted --
  type        (button|submit|reset) submit -- for use as form button --
  disabled    (disabled)     #IMPLIED  -- unavailable in this context --
  tabindex    NUMBER         #IMPLIED  -- position in tabbing order --
  accesskey   %Character;    #IMPLIED  -- accessibility key character --
  onfocus     %Script;       #IMPLIED  -- the element got the focus --
  onblur      %Script;       #IMPLIED  -- the element lost the focus --
  %reserved;                           -- reserved for possible future use --
  >

<!--======================= Tables =======================================-->

<!-- IETF HTML table standard, see [RFC1942] -->

<!--
 The BORDER attribute sets the thickness of the frame around the
 table. The default units are screen pixels.

 The FRAME attribute specifies which parts of the frame around
 the table should be rendered. The values are not the same as
 CALS to avoid a name clash with the VALIGN attribute.

 The value "border" is included for backwards compatibility with
 <TABLE BORDER> which yields frame=border and border=implied
 For <TABLE BORDER=1> you get border=1 and frame=implied. In this
 case, it is appropriate to treat this as frame=border for backwards
 compatibility with deployed browsers.
-->
<!ENTITY % TFrame "(void|above|below|hsides|lhs|rhs|vsides|box|border)">

<!--
 The RULES attribute defines which rules to draw between cells:

 If RULES is absent then assume:
     "none" if BORDER is absent or BORDER=0 otherwise "all"
-->

<!ENTITY % TRules "(none | groups | rows | cols | all)">

<!-- horizontal placement of table relative to document -->
<!ENTITY % TAlign "(left|center|right)">

<!-- horizontal alignment attributes for cell contents -->
<!ENTITY % cellhalign
  "align      (left|center|right|justify|char) #IMPLIED
   char       %Character;    #IMPLIED  -- alignment char, e.g. char=':' --
   charoff    %Length;       #IMPLIED  -- offset for alignment char --"
  >

<!-- vertical alignment attributes for cell contents -->
<!ENTITY % cellvalign
  "valign     (top|middle|bottom|baseline) #IMPLIED"
  >

<!ELEMENT TABLE - -
     (CAPTION?, (COL*|COLGROUP*), THEAD?, TFOOT?, TBODY+)>
<!ELEMENT CAPTION  - - (%inline;)*     -- table caption -->
<!ELEMENT THEAD    - O (TR)+           -- table header -->
<!ELEMENT TFOOT    - O (TR)+           -- table footer -->
<!ELEMENT TBODY    O O (TR)+           -- table body -->
<!ELEMENT COLGROUP - O (col)*          -- table column group -->
<!ELEMENT COL      - O EMPTY           -- table column -->
<!ELEMENT TR       - O (TH|TD)+        -- table row -->
<!ELEMENT (TH|TD)  - O (%flow;)*       -- table header cell, table data cell-->

<!ATTLIST TABLE                        -- table element --
  %attrs;                              -- %coreattrs, %i18n, %events --
  summary     %Text;         #IMPLIED  -- purpose/structure for speech output--
  width       %Length;       #IMPLIED  -- table width --
  border      %Pixels;       #IMPLIED  -- controls frame width around table --
  frame       %TFrame;       #IMPLIED  -- which parts of frame to render --
  rules       %TRules;       #IMPLIED  -- rulings between rows and cols --
  cellspacing %Length;       #IMPLIED  -- spacing between cells --
  cellpadding %Length;       #IMPLIED  -- spacing within cells --
  align       %TAlign;       #IMPLIED  -- table position relative to window --
  bgcolor     %Color;        #IMPLIED  -- background color for cells --
  %reserved;                           -- reserved for possible future use --
  datapagesize CDATA         #IMPLIED  -- reserved for possible future use --
  >

<!ENTITY % CAlign "(top|bottom|left|right)">

<!ATTLIST CAPTION
  %attrs;                              -- %coreattrs, %i18n, %events --
  align       %CAlign;       #IMPLIED  -- relative to table --
  >

<!--
COLGROUP groups a set of COL elements. It allows you to group
several semantically related columns together.
-->
<!ATTLIST COLGROUP
  %attrs;                              -- %coreattrs, %i18n, %events --
  span        NUMBER         1         -- default number of columns in group --
  width       %MultiLength;  #IMPLIED  -- default width for enclosed COLs --
  %cellhalign;                         -- horizontal alignment in cells --
  %cellvalign;                         -- vertical alignment in cells --
  >

<!--
 COL elements define the alignment properties for cells in
 one or more columns.

 The WIDTH attribute specifies the width of the columns, e.g.

     width=64        width in screen pixels
     width=0.5*      relative width of 0.5

 The SPAN attribute causes the attributes of one
 COL element to apply to more than one column.
-->
<!ATTLIST COL                          -- column groups and properties --
  %attrs;                              -- %coreattrs, %i18n, %events --
  span        NUMBER         1         -- COL attributes affect N columns --
  width       %MultiLength;  #IMPLIED  -- column width specification --
  %cellhalign;                         -- horizontal alignment in cells --
  %cellvalign;                         -- vertical alignment in cells --
  >

<!--
    Use THEAD to duplicate headers when breaking table
    across page boundaries, or for static headers when
    TBODY sections are rendered in scrolling panel.

    Use TFOOT to duplicate footers when breaking table
    across page boundaries, or for static footers when
    TBODY sections are rendered in scrolling panel.

    Use multiple TBODY sections when rules are needed
    between groups of table rows.
-->
<!ATTLIST (THEAD|TBODY|TFOOT)          -- table section --
  %attrs;                              -- %coreattrs, %i18n, %events --
  %cellhalign;                         -- horizontal alignment in cells --
  %cellvalign;                         -- vertical alignment in cells --
  >

<!ATTLIST TR                           -- table row --
  %attrs;                              -- %coreattrs, %i18n, %events --
  %cellhalign;                         -- horizontal alignment in cells --
  %cellvalign;                         -- vertical alignment in cells --
  bgcolor     %Color;        #IMPLIED  -- background color for row --
  >

<!-- Scope is simpler than axes attribute for common tables -->
<!ENTITY % Scope "(row|col|rowgroup|colgroup)">

<!-- TH is for headers, TD for data, but for cells acting as both use TD -->
<!ATTLIST (TH|TD)                      -- header or data cell --
  %attrs;                              -- %coreattrs, %i18n, %events --
  abbr        %Text;         #IMPLIED  -- abbreviation for header cell --
  axis        CDATA          #IMPLIED  -- names groups of related headers--
  headers     IDREFS         #IMPLIED  -- list of id's for header cells --
  scope       %Scope;        #IMPLIED  -- scope covered by header cells --
  rowspan     NUMBER         1         -- number of rows spanned by cell --
  colspan     NUMBER         1         -- number of cols spanned by cell --
  %cellhalign;                         -- horizontal alignment in cells --
  %cellvalign;                         -- vertical alignment in cells --
  nowrap      (nowrap)       #IMPLIED  -- suppress word wrap --
  bgcolor     %Color;        #IMPLIED  -- cell background color --
  width       %Pixels;       #IMPLIED  -- width for cell --
  height      %Pixels;       #IMPLIED  -- height for cell --
  >

<!--================== Document Frames ===================================-->

<!--
  The content model for HTML documents depends on whether the HEAD is
  followed by a FRAMESET or BODY element. The widespread omission of
  the BODY start tag makes it impractical to define the content model
  without the use of a marked section.
-->

<!-- Feature Switch for frameset documents -->
<!ENTITY % HTML.Frameset "IGNORE">

<![ %HTML.Frameset; [
<!ELEMENT FRAMESET - - ((FRAMESET|FRAME)+ & NOFRAMES?) -- window subdivision-->
<!ATTLIST FRAMESET
  %coreattrs;                          -- id, class, style, title --
  rows        %MultiLengths; #IMPLIED  -- list of lengths,
                                          default: 100% (1 row) --
  cols        %MultiLengths; #IMPLIED  -- list of lengths,
                                          default: 100% (1 col) --
  onload      %Script;       #IMPLIED  -- all the frames have been loaded  --
  onunload    %Script;       #IMPLIED  -- all the frames have been removed --
  >
]]>

<![ %HTML.Frameset; [
<!-- reserved frame names start with "_" otherwise starts with letter -->
<!ELEMENT FRAME - O EMPTY              -- subwindow -->
<!ATTLIST FRAME
  %coreattrs;                          -- id, class, style, title --
  longdesc    %URI;          #IMPLIED  -- link to long description
                                          (complements title) --
  name        CDATA          #IMPLIED  -- name of frame for targetting --
  src         %URI;          #IMPLIED  -- source of frame content --
  frameborder (1|0)          1         -- request frame borders? --
  marginwidth %Pixels;       #IMPLIED  -- margin widths in pixels --
  marginheight %Pixels;      #IMPLIED  -- margin height in pixels --
  noresize    (noresize)     #IMPLIED  -- allow users to resize frames? --
  scrolling   (yes|no|auto)  auto      -- scrollbar or none --
  >
]]>

<!ELEMENT IFRAME - - (%flow;)*         -- inline subwindow -->
<!ATTLIST IFRAME
  %coreattrs;                          -- id, class, style, title --
  longdesc    %URI;          #IMPLIED  -- link to long description
                                          (complements title) --
  name        CDATA          #IMPLIED  -- name of frame for targetting --
  src         %URI;          #IMPLIED  -- source of frame content --
  frameborder (1|0)          1         -- request frame borders? --
  marginwidth %Pixels;       #IMPLIED  -- margin widths in pixels --
  marginheight %Pixels;      #IMPLIED  -- margin height in pixels --
  scrolling   (yes|no|auto)  auto      -- scrollbar or none --
  align       %IAlign;       #IMPLIED  -- vertical or horizontal alignment --
  height      %Length;       #IMPLIED  -- frame height --
  width       %Length;       #IMPLIED  -- frame width --
  >

<![ %HTML.Frameset; [
<!ENTITY % noframes.content "(BODY) -(NOFRAMES)">
]]>

<!ENTITY % noframes.content "(%flow;)*">

<!ELEMENT NOFRAMES - - %noframes.content;
 -- alternate content container for non frame-based rendering -->
<!ATTLIST NOFRAMES
  %attrs;                              -- %coreattrs, %i18n, %events --
  >

<!--================ Document Head =======================================-->
<!-- %head.misc; defined earlier on as "SCRIPT|STYLE|META|LINK|OBJECT" -->
<!ENTITY % head.content "TITLE & ISINDEX? & BASE?">

<!ELEMENT HEAD O O (%head.content;) +(%head.misc;) -- document head -->
<!ATTLIST HEAD
  %i18n;                               -- lang, dir --
  profile     %URI;          #IMPLIED  -- named dictionary of meta info --
  >

<!-- The TITLE element is not considered part of the flow of text.
       It should be displayed, for example as the page header or
       window title. Exactly one title is required per document.
    -->
<!ELEMENT TITLE - - (#PCDATA) -(%head.misc;) -- document title -->
<!ATTLIST TITLE %i18n>

<!ELEMENT ISINDEX - O EMPTY            -- single line prompt -->
<!ATTLIST ISINDEX
  %coreattrs;                          -- id, class, style, title --
  %i18n;                               -- lang, dir --
  prompt      %Text;         #IMPLIED  -- prompt message -->

<!ELEMENT BASE - O EMPTY               -- document base URI -->
<!ATTLIST BASE
  href        %URI;          #IMPLIED  -- URI that acts as base URI --
  target      %FrameTarget;  #IMPLIED  -- render in this frame --
  >

<!ELEMENT META - O EMPTY               -- generic metainformation -->
<!ATTLIST META
  %i18n;                               -- lang, dir, for use with content --
  http-equiv  NAME           #IMPLIED  -- HTTP response header name  --
  name        NAME           #IMPLIED  -- metainformation name --
  content     CDATA          #REQUIRED -- associated information --
  scheme      CDATA          #IMPLIED  -- select form of content --
  >

<!ELEMENT STYLE - - %StyleSheet        -- style info -->
<!ATTLIST STYLE
  %i18n;                               -- lang, dir, for use with title --
  type        %ContentType;  #REQUIRED -- content type of style language --
  media       %MediaDesc;    #IMPLIED  -- designed for use with these media --
  title       %Text;         #IMPLIED  -- advisory title --
  >

<!ELEMENT SCRIPT - - %Script;          -- script statements -->
<!ATTLIST SCRIPT
  charset     %Charset;      #IMPLIED  -- char encoding of linked resource --
  type        %ContentType;  #REQUIRED -- content type of script language --
  language    CDATA          #IMPLIED  -- predefined script language name --
  src         %URI;          #IMPLIED  -- URI for an external script --
  defer       (defer)        #IMPLIED  -- UA may defer execution of script --
  event       CDATA          #IMPLIED  -- reserved for possible future use --
  for         %URI;          #IMPLIED  -- reserved for possible future use --
  >

<!ELEMENT NOSCRIPT - - (%flow;)*
  -- alternate content container for non script-based rendering -->
<!ATTLIST NOSCRIPT
  %attrs;                              -- %coreattrs, %i18n, %events --
  >

<!--================ Document Structure ==================================-->
<!ENTITY % version "version CDATA #FIXED '%HTML.Version;'">

<![ %HTML.Frameset; [
<!ENTITY % html.content "HEAD, FRAMESET">
]]>

<!ENTITY % html.content "HEAD, BODY">

<!ELEMENT HTML O O (%html.content;)    -- document root element -->
<!ATTLIST HTML
  %i18n;                               -- lang, dir --
  %version;
  >

                    23 Frameset Document Type Definition

<!--
    This is the HTML 4.0 Frameset DTD, which should be
    used for documents with frames. This DTD is identical
    to the HTML 4.0 Transitional DTD except for the
    content model of the "HTML" element: in frameset
    documents, the "FRAMESET" element replaces the "BODY"
    element.

          Draft: $Date: 1997/12/11 15:31:11 $

          Authors:
              Dave Raggett <dsr@w3.org>
              Arnaud Le Hors <lehors@w3.org>
              Ian Jacobs <ij@w3.org>

    Further information about HTML 4.0 is available at:

          http://www.w3.org/TR/REC-html40.
-->
<!ENTITY % HTML.Version "-//W3C//DTD HTML 4.0 Frameset//EN"
  -- Typical usage:

    <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Frameset//EN"
            "http://www.w3.org/TR/REC-html40/frameset.dtd">
    <html>
    <head>
    ...
    </head>
    <frameset>
    ...
    </frameset>
    </html>
-->

<!ENTITY % HTML.Frameset "INCLUDE">
<!ENTITY % HTML4.dtd PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
%HTML4.dtd;

                 24 Character entity references in HTML 4.0

Contents

  1. Introduction to character entity references
  2. Character entity references for ISO 8859-1 characters
       1. The list of characters
  3. Character entity references for symbols, mathematical symbols, and
     Greek letters
       1. The list of characters
  4. Character entity references for markup-significant and
     internationalization characters
       1. The list of characters

24.1 Introduction to character entity references

A character entity reference is an SGML construct that references a
character of the document character set.

This version of HTML supports several sets of character entity references:

   * ISO 8859-1 (Latin-1) characters In accordance with section 14 of
     [RFC1866], the set of Latin-1 entities has been extended by this
     specification to cover the whole right part of ISO-8859-1 (all code
     positions with the high-order bit set), including the already commonly
     used &nbsp;, &copy; and &reg;. The names of the entities are taken from
     the appendices of SGML (defined in [ISO8879]).
   * symbols, mathematical symbols, and Greek letters. These characters may
     be represented by glyphs in the Adobe font "Symbol".
   * markup-significant and internationalization characters (e.g., for
     bidirectional text).

The following sections present the complete lists of character entity
references. Although by convention, [ISO10646] names are written with upper
case letters, we have converted them to lower case in this specification for
reasons of readability.

24.2 Character entity references for ISO 8859-1 characters

The character entity references in this section produce characters whose
numeric equivalents should already be supported by conforming HTML 2.0 user
agents. Thus, the character entity reference &divide; is a more convenient
form than &#247; for obtaining the division sign (÷).

To support these named entities, user agents need only recognize the entity
names and convert them to characters that lie within the repertoire of
[ISO88591].

Character 65533 (FFFD hexadecimal) is the last valid character in UCS-2.
65534 (FFFE hexadecimal) is unassigned and reserved as the byte-swapped
version of ZERO WIDTH NON-BREAKING SPACE for byte-order detection purposes.
65535 (FFFF hexadecimal) is unassigned.

24.2.1 The list of characters

<!-- Portions © International Organization for Standardization 1986
     Permission to copy in any form is granted for use with
     conforming SGML systems and applications as defined in
     ISO 8879, provided this notice is included in all copies.
-->
<!-- Character entity set. Typical invocation:
     <!ENTITY % HTMLlat1 PUBLIC
       "-//W3C//ENTITIES Full Latin 1//EN//HTML">
     %HTMLlat1;
-->

<!ENTITY nbsp   CDATA "&#160;" -- no-break space = non-breaking space,
                                  U+00A0 ISOnum -->
<!ENTITY iexcl  CDATA "&#161;" -- inverted exclamation mark, U+00A1 ISOnum -->
<!ENTITY cent   CDATA "&#162;" -- cent sign, U+00A2 ISOnum -->
<!ENTITY pound  CDATA "&#163;" -- pound sign, U+00A3 ISOnum -->
<!ENTITY curren CDATA "&#164;" -- currency sign, U+00A4 ISOnum -->
<!ENTITY yen    CDATA "&#165;" -- yen sign = yuan sign, U+00A5 ISOnum -->
<!ENTITY brvbar CDATA "&#166;" -- broken bar = broken vertical bar,
                                  U+00A6 ISOnum -->
<!ENTITY sect   CDATA "&#167;" -- section sign, U+00A7 ISOnum -->
<!ENTITY uml    CDATA "&#168;" -- diaeresis = spacing diaeresis,
                                  U+00A8 ISOdia -->
<!ENTITY copy   CDATA "&#169;" -- copyright sign, U+00A9 ISOnum -->
<!ENTITY ordf   CDATA "&#170;" -- feminine ordinal indicator, U+00AA ISOnum -->
<!ENTITY laquo  CDATA "&#171;" -- left-pointing double angle quotation mark
                                  = left pointing guillemet, U+00AB ISOnum -->
<!ENTITY not    CDATA "&#172;" -- not sign = discretionary hyphen,
                                  U+00AC ISOnum -->
<!ENTITY shy    CDATA "&#173;" -- soft hyphen = discretionary hyphen,
                                  U+00AD ISOnum -->
<!ENTITY reg    CDATA "&#174;" -- registered sign = registered trade mark sign,
                                  U+00AE ISOnum -->
<!ENTITY macr   CDATA "&#175;" -- macron = spacing macron = overline
                                  = APL overbar, U+00AF ISOdia -->
<!ENTITY deg    CDATA "&#176;" -- degree sign, U+00B0 ISOnum -->
<!ENTITY plusmn CDATA "&#177;" -- plus-minus sign = plus-or-minus sign,
                                  U+00B1 ISOnum -->
<!ENTITY sup2   CDATA "&#178;" -- superscript two = superscript digit two
                                  = squared, U+00B2 ISOnum -->
<!ENTITY sup3   CDATA "&#179;" -- superscript three = superscript digit three
                                  = cubed, U+00B3 ISOnum -->
<!ENTITY acute  CDATA "&#180;" -- acute accent = spacing acute,
                                  U+00B4 ISOdia -->
<!ENTITY micro  CDATA "&#181;" -- micro sign, U+00B5 ISOnum -->
<!ENTITY para   CDATA "&#182;" -- pilcrow sign = paragraph sign,
                                  U+00B6 ISOnum -->
<!ENTITY middot CDATA "&#183;" -- middle dot = Georgian comma
                                  = Greek middle dot, U+00B7 ISOnum -->
<!ENTITY cedil  CDATA "&#184;" -- cedilla = spacing cedilla, U+00B8 ISOdia -->
<!ENTITY sup1   CDATA "&#185;" -- superscript one = superscript digit one,
                                  U+00B9 ISOnum -->
<!ENTITY ordm   CDATA "&#186;" -- masculine ordinal indicator,
                                  U+00BA ISOnum -->
<!ENTITY raquo  CDATA "&#187;" -- right-pointing double angle quotation mark
                                  = right pointing guillemet, U+00BB ISOnum -->
<!ENTITY frac14 CDATA "&#188;" -- vulgar fraction one quarter
                                  = fraction one quarter, U+00BC ISOnum -->
<!ENTITY frac12 CDATA "&#189;" -- vulgar fraction one half
                                  = fraction one half, U+00BD ISOnum -->
<!ENTITY frac34 CDATA "&#190;" -- vulgar fraction three quarters
                                  = fraction three quarters, U+00BE ISOnum -->
<!ENTITY iquest CDATA "&#191;" -- inverted question mark
                                  = turned question mark, U+00BF ISOnum -->
<!ENTITY Agrave CDATA "&#192;" -- latin capital letter A with grave
                                  = latin capital letter A grave,
                                  U+00C0 ISOlat1 -->
<!ENTITY Aacute CDATA "&#193;" -- latin capital letter A with acute,
                                  U+00C1 ISOlat1 -->
<!ENTITY Acirc  CDATA "&#194;" -- latin capital letter A with circumflex,
                                  U+00C2 ISOlat1 -->
<!ENTITY Atilde CDATA "&#195;" -- latin capital letter A with tilde,
                                  U+00C3 ISOlat1 -->
<!ENTITY Auml   CDATA "&#196;" -- latin capital letter A with diaeresis,
                                  U+00C4 ISOlat1 -->
<!ENTITY Aring  CDATA "&#197;" -- latin capital letter A with ring above
                                  = latin capital letter A ring,
                                  U+00C5 ISOlat1 -->
<!ENTITY AElig  CDATA "&#198;" -- latin capital letter AE
                                  = latin capital ligature AE,
                                  U+00C6 ISOlat1 -->
<!ENTITY Ccedil CDATA "&#199;" -- latin capital letter C with cedilla,
                                  U+00C7 ISOlat1 -->
<!ENTITY Egrave CDATA "&#200;" -- latin capital letter E with grave,
                                  U+00C8 ISOlat1 -->
<!ENTITY Eacute CDATA "&#201;" -- latin capital letter E with acute,
                                  U+00C9 ISOlat1 -->
<!ENTITY Ecirc  CDATA "&#202;" -- latin capital letter E with circumflex,
                                  U+00CA ISOlat1 -->
<!ENTITY Euml   CDATA "&#203;" -- latin capital letter E with diaeresis,
                                  U+00CB ISOlat1 -->
<!ENTITY Igrave CDATA "&#204;" -- latin capital letter I with grave,
                                  U+00CC ISOlat1 -->
<!ENTITY Iacute CDATA "&#205;" -- latin capital letter I with acute,
                                  U+00CD ISOlat1 -->
<!ENTITY Icirc  CDATA "&#206;" -- latin capital letter I with circumflex,
                                  U+00CE ISOlat1 -->
<!ENTITY Iuml   CDATA "&#207;" -- latin capital letter I with diaeresis,
                                  U+00CF ISOlat1 -->
<!ENTITY ETH    CDATA "&#208;" -- latin capital letter ETH, U+00D0 ISOlat1 -->
<!ENTITY Ntilde CDATA "&#209;" -- latin capital letter N with tilde,
                                  U+00D1 ISOlat1 -->
<!ENTITY Ograve CDATA "&#210;" -- latin capital letter O with grave,
                                  U+00D2 ISOlat1 -->
<!ENTITY Oacute CDATA "&#211;" -- latin capital letter O with acute,
                                  U+00D3 ISOlat1 -->
<!ENTITY Ocirc  CDATA "&#212;" -- latin capital letter O with circumflex,
                                  U+00D4 ISOlat1 -->
<!ENTITY Otilde CDATA "&#213;" -- latin capital letter O with tilde,
                                  U+00D5 ISOlat1 -->
<!ENTITY Ouml   CDATA "&#214;" -- latin capital letter O with diaeresis,
                                  U+00D6 ISOlat1 -->
<!ENTITY times  CDATA "&#215;" -- multiplication sign, U+00D7 ISOnum -->
<!ENTITY Oslash CDATA "&#216;" -- latin capital letter O with stroke
                                  = latin capital letter O slash,
                                  U+00D8 ISOlat1 -->
<!ENTITY Ugrave CDATA "&#217;" -- latin capital letter U with grave,
                                  U+00D9 ISOlat1 -->
<!ENTITY Uacute CDATA "&#218;" -- latin capital letter U with acute,
                                  U+00DA ISOlat1 -->
<!ENTITY Ucirc  CDATA "&#219;" -- latin capital letter U with circumflex,
                                  U+00DB ISOlat1 -->
<!ENTITY Uuml   CDATA "&#220;" -- latin capital letter U with diaeresis,
                                  U+00DC ISOlat1 -->
<!ENTITY Yacute CDATA "&#221;" -- latin capital letter Y with acute,
                                  U+00DD ISOlat1 -->
<!ENTITY THORN  CDATA "&#222;" -- latin capital letter THORN,
                                  U+00DE ISOlat1 -->
<!ENTITY szlig  CDATA "&#223;" -- latin small letter sharp s = ess-zed,
                                  U+00DF ISOlat1 -->
<!ENTITY agrave CDATA "&#224;" -- latin small letter a with grave
                                  = latin small letter a grave,
                                  U+00E0 ISOlat1 -->
<!ENTITY aacute CDATA "&#225;" -- latin small letter a with acute,
                                  U+00E1 ISOlat1 -->
<!ENTITY acirc  CDATA "&#226;" -- latin small letter a with circumflex,
                                  U+00E2 ISOlat1 -->
<!ENTITY atilde CDATA "&#227;" -- latin small letter a with tilde,
                                  U+00E3 ISOlat1 -->
<!ENTITY auml   CDATA "&#228;" -- latin small letter a with diaeresis,
                                  U+00E4 ISOlat1 -->
<!ENTITY aring  CDATA "&#229;" -- latin small letter a with ring above
                                  = latin small letter a ring,
                                  U+00E5 ISOlat1 -->
<!ENTITY aelig  CDATA "&#230;" -- latin small letter ae
                                  = latin small ligature ae, U+00E6 ISOlat1 -->
<!ENTITY ccedil CDATA "&#231;" -- latin small letter c with cedilla,
                                  U+00E7 ISOlat1 -->
<!ENTITY egrave CDATA "&#232;" -- latin small letter e with grave,
                                  U+00E8 ISOlat1 -->
<!ENTITY eacute CDATA "&#233;" -- latin small letter e with acute,
                                  U+00E9 ISOlat1 -->
<!ENTITY ecirc  CDATA "&#234;" -- latin small letter e with circumflex,
                                  U+00EA ISOlat1 -->
<!ENTITY euml   CDATA "&#235;" -- latin small letter e with diaeresis,
                                  U+00EB ISOlat1 -->
<!ENTITY igrave CDATA "&#236;" -- latin small letter i with grave,
                                  U+00EC ISOlat1 -->
<!ENTITY iacute CDATA "&#237;" -- latin small letter i with acute,
                                  U+00ED ISOlat1 -->
<!ENTITY icirc  CDATA "&#238;" -- latin small letter i with circumflex,
                                  U+00EE ISOlat1 -->
<!ENTITY iuml   CDATA "&#239;" -- latin small letter i with diaeresis,
                                  U+00EF ISOlat1 -->
<!ENTITY eth    CDATA "&#240;" -- latin small letter eth, U+00F0 ISOlat1 -->
<!ENTITY ntilde CDATA "&#241;" -- latin small letter n with tilde,
                                  U+00F1 ISOlat1 -->
<!ENTITY ograve CDATA "&#242;" -- latin small letter o with grave,
                                  U+00F2 ISOlat1 -->
<!ENTITY oacute CDATA "&#243;" -- latin small letter o with acute,
                                  U+00F3 ISOlat1 -->
<!ENTITY ocirc  CDATA "&#244;" -- latin small letter o with circumflex,
                                  U+00F4 ISOlat1 -->
<!ENTITY otilde CDATA "&#245;" -- latin small letter o with tilde,
                                  U+00F5 ISOlat1 -->
<!ENTITY ouml   CDATA "&#246;" -- latin small letter o with diaeresis,
                                  U+00F6 ISOlat1 -->
<!ENTITY divide CDATA "&#247;" -- division sign, U+00F7 ISOnum -->
<!ENTITY oslash CDATA "&#248;" -- latin small letter o with stroke,
                                  = latin small letter o slash,
                                  U+00F8 ISOlat1 -->
<!ENTITY ugrave CDATA "&#249;" -- latin small letter u with grave,
                                  U+00F9 ISOlat1 -->
<!ENTITY uacute CDATA "&#250;" -- latin small letter u with acute,
                                  U+00FA ISOlat1 -->
<!ENTITY ucirc  CDATA "&#251;" -- latin small letter u with circumflex,
                                  U+00FB ISOlat1 -->
<!ENTITY uuml   CDATA "&#252;" -- latin small letter u with diaeresis,
                                  U+00FC ISOlat1 -->
<!ENTITY yacute CDATA "&#253;" -- latin small letter y with acute,
                                  U+00FD ISOlat1 -->
<!ENTITY thorn  CDATA "&#254;" -- latin small letter thorn with,
                                  U+00FE ISOlat1 -->
<!ENTITY yuml   CDATA "&#255;" -- latin small letter y with diaeresis,
                                  U+00FF ISOlat1 -->

24.3 Character entity references for symbols, mathematical symbols, and
Greek letters

The character entity references in this section produce characters that may
be represented by glyphs in the widely available Adobe Symbol font,
including Greek characters, various bracketing symbols, and a selection of
mathematical operators such as gradient, product, and summation symbols.

To support these entities, user agents may support full [ISO10646] or use
other means. Display of glyphs for these characters may be obtained by being
able to display the relevant [ISO10646] characters or by other means, such
as internally mapping the listed entities, numeric character references, and
characters to the appropriate position in some font that contains the
requisite glyphs.

When to use Greek entities. This entity set contains all the letters used in
modern Greek. However, it does not include Greek punctuation, precomposed
accented characters nor the non-spacing accents (tonos, dialytika) required
to compose them. There are no archaic letters, Coptic-unique letters, or
precomposed letters for Polytonic Greek. The entities defined here are not
intended for the representation of modern Greek text and would not be an
efficient representation; rather, they are intended for occasional Greek
letters used in technical and mathematical works.

24.3.1 The list of characters

<!-- Mathematical, Greek and Symbolic characters for HTML -->

<!-- Character entity set. Typical invocation:
     <!ENTITY % HTMLsymbol PUBLIC
       "-//W3C//ENTITIES Symbolic//EN//HTML">
     %HTMLsymbol; -->

<!-- Portions © International Organization for Standardization 1986:
     Permission to copy in any form is granted for use with
     conforming SGML systems and applications as defined in
     ISO 8879, provided this notice is included in all copies.
-->

<!-- Relevant ISO entity set is given unless names are newly introduced.
     New names (i.e., not in ISO 8879 list) do not clash with any
     existing ISO 8879 entity names. ISO 10646 character numbers
     are given for each character, in hex. CDATA values are decimal
     conversions of the ISO 10646 values and refer to the document
     character set. Names are Unicode 2.0 names.

-->

<!-- Latin Extended-B -->
<!ENTITY fnof     CDATA "&#402;" -- latin small f with hook = function
                                    = florin, U+0192 ISOtech -->

<!-- Greek -->
<!ENTITY Alpha    CDATA "&#913;" -- greek capital letter alpha, U+0391 -->
<!ENTITY Beta     CDATA "&#914;" -- greek capital letter beta, U+0392 -->
<!ENTITY Gamma    CDATA "&#915;" -- greek capital letter gamma,
                                    U+0393 ISOgrk3 -->
<!ENTITY Delta    CDATA "&#916;" -- greek capital letter delta,
                                    U+0394 ISOgrk3 -->
<!ENTITY Epsilon  CDATA "&#917;" -- greek capital letter epsilon, U+0395 -->
<!ENTITY Zeta     CDATA "&#918;" -- greek capital letter zeta, U+0396 -->
<!ENTITY Eta      CDATA "&#919;" -- greek capital letter eta, U+0397 -->
<!ENTITY Theta    CDATA "&#920;" -- greek capital letter theta,
                                    U+0398 ISOgrk3 -->
<!ENTITY Iota     CDATA "&#921;" -- greek capital letter iota, U+0399 -->
<!ENTITY Kappa    CDATA "&#922;" -- greek capital letter kappa, U+039A -->
<!ENTITY Lambda   CDATA "&#923;" -- greek capital letter lambda,
                                    U+039B ISOgrk3 -->
<!ENTITY Mu       CDATA "&#924;" -- greek capital letter mu, U+039C -->
<!ENTITY Nu       CDATA "&#925;" -- greek capital letter nu, U+039D -->
<!ENTITY Xi       CDATA "&#926;" -- greek capital letter xi, U+039E ISOgrk3 -->
<!ENTITY Omicron  CDATA "&#927;" -- greek capital letter omicron, U+039F -->
<!ENTITY Pi       CDATA "&#928;" -- greek capital letter pi, U+03A0 ISOgrk3 -->
<!ENTITY Rho      CDATA "&#929;" -- greek capital letter rho, U+03A1 -->
<!-- there is no Sigmaf, and no U+03A2 character either -->
<!ENTITY Sigma    CDATA "&#931;" -- greek capital letter sigma,
                                    U+03A3 ISOgrk3 -->
<!ENTITY Tau      CDATA "&#932;" -- greek capital letter tau, U+03A4 -->
<!ENTITY Upsilon  CDATA "&#933;" -- greek capital letter upsilon,
                                    U+03A5 ISOgrk3 -->
<!ENTITY Phi      CDATA "&#934;" -- greek capital letter phi,
                                    U+03A6 ISOgrk3 -->
<!ENTITY Chi      CDATA "&#935;" -- greek capital letter chi, U+03A7 -->
<!ENTITY Psi      CDATA "&#936;" -- greek capital letter psi,
                                    U+03A8 ISOgrk3 -->
<!ENTITY Omega    CDATA "&#937;" -- greek capital letter omega,
                                    U+03A9 ISOgrk3 -->

<!ENTITY alpha    CDATA "&#945;" -- greek small letter alpha,
                                    U+03B1 ISOgrk3 -->
<!ENTITY beta     CDATA "&#946;" -- greek small letter beta, U+03B2 ISOgrk3 -->
<!ENTITY gamma    CDATA "&#947;" -- greek small letter gamma,
                                    U+03B3 ISOgrk3 -->
<!ENTITY delta    CDATA "&#948;" -- greek small letter delta,
                                    U+03B4 ISOgrk3 -->
<!ENTITY epsilon  CDATA "&#949;" -- greek small letter epsilon,
                                    U+03B5 ISOgrk3 -->
<!ENTITY zeta     CDATA "&#950;" -- greek small letter zeta, U+03B6 ISOgrk3 -->
<!ENTITY eta      CDATA "&#951;" -- greek small letter eta, U+03B7 ISOgrk3 -->
<!ENTITY theta    CDATA "&#952;" -- greek small letter theta,
                                    U+03B8 ISOgrk3 -->
<!ENTITY iota     CDATA "&#953;" -- greek small letter iota, U+03B9 ISOgrk3 -->
<!ENTITY kappa    CDATA "&#954;" -- greek small letter kappa,
                                    U+03BA ISOgrk3 -->
<!ENTITY lambda   CDATA "&#955;" -- greek small letter lambda,
                                    U+03BB ISOgrk3 -->
<!ENTITY mu       CDATA "&#956;" -- greek small letter mu, U+03BC ISOgrk3 -->
<!ENTITY nu       CDATA "&#957;" -- greek small letter nu, U+03BD ISOgrk3 -->
<!ENTITY xi       CDATA "&#958;" -- greek small letter xi, U+03BE ISOgrk3 -->
<!ENTITY omicron  CDATA "&#959;" -- greek small letter omicron, U+03BF NEW -->
<!ENTITY pi       CDATA "&#960;" -- greek small letter pi, U+03C0 ISOgrk3 -->
<!ENTITY rho      CDATA "&#961;" -- greek small letter rho, U+03C1 ISOgrk3 -->
<!ENTITY sigmaf   CDATA "&#962;" -- greek small letter final sigma,
                                    U+03C2 ISOgrk3 -->
<!ENTITY sigma    CDATA "&#963;" -- greek small letter sigma,
                                    U+03C3 ISOgrk3 -->
<!ENTITY tau      CDATA "&#964;" -- greek small letter tau, U+03C4 ISOgrk3 -->
<!ENTITY upsilon  CDATA "&#965;" -- greek small letter upsilon,
                                    U+03C5 ISOgrk3 -->
<!ENTITY phi      CDATA "&#966;" -- greek small letter phi, U+03C6 ISOgrk3 -->
<!ENTITY chi      CDATA "&#967;" -- greek small letter chi, U+03C7 ISOgrk3 -->
<!ENTITY psi      CDATA "&#968;" -- greek small letter psi, U+03C8 ISOgrk3 -->
<!ENTITY omega    CDATA "&#969;" -- greek small letter omega,
                                    U+03C9 ISOgrk3 -->
<!ENTITY thetasym CDATA "&#977;" -- greek small letter theta symbol,
                                    U+03D1 NEW -->
<!ENTITY upsih    CDATA "&#978;" -- greek upsilon with hook symbol,
                                    U+03D2 NEW -->
<!ENTITY piv      CDATA "&#982;" -- greek pi symbol, U+03D6 ISOgrk3 -->

<!-- General Punctuation -->
<!ENTITY bull     CDATA "&#8226;" -- bullet = black small circle,
                                     U+2022 ISOpub  -->
<!-- bullet is NOT the same as bullet operator, U+2219 -->
<!ENTITY hellip   CDATA "&#8230;" -- horizontal ellipsis = three dot leader,
                                     U+2026 ISOpub  -->
<!ENTITY prime    CDATA "&#8242;" -- prime = minutes = feet, U+2032 ISOtech -->
<!ENTITY Prime    CDATA "&#8243;" -- double prime = seconds = inches,
                                     U+2033 ISOtech -->
<!ENTITY oline    CDATA "&#8254;" -- overline = spacing overscore,
                                     U+203E NEW -->
<!ENTITY frasl    CDATA "&#8260;" -- fraction slash, U+2044 NEW -->

<!-- Letterlike Symbols -->
<!ENTITY weierp   CDATA "&#8472;" -- script capital P = power set
                                     = Weierstrass p, U+2118 ISOamso -->
<!ENTITY image    CDATA "&#8465;" -- blackletter capital I = imaginary part,
                                     U+2111 ISOamso -->
<!ENTITY real     CDATA "&#8476;" -- blackletter capital R = real part symbol,
                                     U+211C ISOamso -->
<!ENTITY trade    CDATA "&#8482;" -- trade mark sign, U+2122 ISOnum -->
<!ENTITY alefsym  CDATA "&#8501;" -- alef symbol = first transfinite cardinal,
                                     U+2135 NEW -->
<!-- alef symbol is NOT the same as hebrew letter alef,
     U+05D0 although the same glyph could be used to depict both characters -->

<!-- Arrows -->
<!ENTITY larr     CDATA "&#8592;" -- leftwards arrow, U+2190 ISOnum -->
<!ENTITY uarr     CDATA "&#8593;" -- upwards arrow, U+2191 ISOnum-->
<!ENTITY rarr     CDATA "&#8594;" -- rightwards arrow, U+2192 ISOnum -->
<!ENTITY darr     CDATA "&#8595;" -- downwards arrow, U+2193 ISOnum -->
<!ENTITY harr     CDATA "&#8596;" -- left right arrow, U+2194 ISOamsa -->
<!ENTITY crarr    CDATA "&#8629;" -- downwards arrow with corner leftwards
                                     = carriage return, U+21B5 NEW -->
<!ENTITY lArr     CDATA "&#8656;" -- leftwards double arrow, U+21D0 ISOtech -->
<!-- Unicode does not say that lArr is the same as the 'is implied by' arrow
    but also does not have any other character for that function. So ? lArr can
    be used for 'is implied by' as ISOtech suggests -->
<!ENTITY uArr     CDATA "&#8657;" -- upwards double arrow, U+21D1 ISOamsa -->
<!ENTITY rArr     CDATA "&#8658;" -- rightwards double arrow,
                                     U+21D2 ISOtech -->
<!-- Unicode does not say this is the 'implies' character but does not have
     another character with this function so ?
     rArr can be used for 'implies' as ISOtech suggests -->
<!ENTITY dArr     CDATA "&#8659;" -- downwards double arrow, U+21D3 ISOamsa -->
<!ENTITY hArr     CDATA "&#8660;" -- left right double arrow,
                                     U+21D4 ISOamsa -->

<!-- Mathematical Operators -->
<!ENTITY forall   CDATA "&#8704;" -- for all, U+2200 ISOtech -->
<!ENTITY part     CDATA "&#8706;" -- partial differential, U+2202 ISOtech  -->
<!ENTITY exist    CDATA "&#8707;" -- there exists, U+2203 ISOtech -->
<!ENTITY empty    CDATA "&#8709;" -- empty set = null set = diameter,
                                     U+2205 ISOamso -->
<!ENTITY nabla    CDATA "&#8711;" -- nabla = backward difference,
                                     U+2207 ISOtech -->
<!ENTITY isin     CDATA "&#8712;" -- element of, U+2208 ISOtech -->
<!ENTITY notin    CDATA "&#8713;" -- not an element of, U+2209 ISOtech -->
<!ENTITY ni       CDATA "&#8715;" -- contains as member, U+220B ISOtech -->
<!-- should there be a more memorable name than 'ni'? -->
<!ENTITY prod     CDATA "&#8719;" -- n-ary product = product sign,
                                     U+220F ISOamsb -->
<!-- prod is NOT the same character as U+03A0 'greek capital letter pi' though
     the same glyph might be used for both -->
<!ENTITY sum      CDATA "&#8721;" -- n-ary sumation, U+2211 ISOamsb -->
<!-- sum is NOT the same character as U+03A3 'greek capital letter sigma'
     though the same glyph might be used for both -->
<!ENTITY minus    CDATA "&#8722;" -- minus sign, U+2212 ISOtech -->
<!ENTITY lowast   CDATA "&#8727;" -- asterisk operator, U+2217 ISOtech -->
<!ENTITY radic    CDATA "&#8730;" -- square root = radical sign,
                                     U+221A ISOtech -->
<!ENTITY prop     CDATA "&#8733;" -- proportional to, U+221D ISOtech -->
<!ENTITY infin    CDATA "&#8734;" -- infinity, U+221E ISOtech -->
<!ENTITY ang      CDATA "&#8736;" -- angle, U+2220 ISOamso -->
<!ENTITY and      CDATA "&#8743;" -- logical and = wedge, U+2227 ISOtech -->
<!ENTITY or       CDATA "&#8744;" -- logical or = vee, U+2228 ISOtech -->
<!ENTITY cap      CDATA "&#8745;" -- intersection = cap, U+2229 ISOtech -->
<!ENTITY cup      CDATA "&#8746;" -- union = cup, U+222A ISOtech -->
<!ENTITY int      CDATA "&#8747;" -- integral, U+222B ISOtech -->
<!ENTITY there4   CDATA "&#8756;" -- therefore, U+2234 ISOtech -->
<!ENTITY sim      CDATA "&#8764;" -- tilde operator = varies with = similar to,
                                     U+223C ISOtech -->
<!-- tilde operator is NOT the same character as the tilde, U+007E,
     although the same glyph might be used to represent both  -->
<!ENTITY cong     CDATA "&#8773;" -- approximately equal to, U+2245 ISOtech -->
<!ENTITY asymp    CDATA "&#8776;" -- almost equal to = asymptotic to,
                                     U+2248 ISOamsr -->
<!ENTITY ne       CDATA "&#8800;" -- not equal to, U+2260 ISOtech -->
<!ENTITY equiv    CDATA "&#8801;" -- identical to, U+2261 ISOtech -->
<!ENTITY le       CDATA "&#8804;" -- less-than or equal to, U+2264 ISOtech -->
<!ENTITY ge       CDATA "&#8805;" -- greater-than or equal to,
                                     U+2265 ISOtech -->
<!ENTITY sub      CDATA "&#8834;" -- subset of, U+2282 ISOtech -->
<!ENTITY sup      CDATA "&#8835;" -- superset of, U+2283 ISOtech -->
<!-- note that nsup, 'not a superset of, U+2283' is not covered by the Symbol
     font encoding and is not included. Should it be, for symmetry?
     It is in ISOamsn  -->
<!ENTITY nsub     CDATA "&#8836;" -- not a subset of, U+2284 ISOamsn -->
<!ENTITY sube     CDATA "&#8838;" -- subset of or equal to, U+2286 ISOtech -->
<!ENTITY supe     CDATA "&#8839;" -- superset of or equal to,
                                     U+2287 ISOtech -->
<!ENTITY oplus    CDATA "&#8853;" -- circled plus = direct sum,
                                     U+2295 ISOamsb -->
<!ENTITY otimes   CDATA "&#8855;" -- circled times = vector product,
                                     U+2297 ISOamsb -->
<!ENTITY perp     CDATA "&#8869;" -- up tack = orthogonal to = perpendicular,
                                     U+22A5 ISOtech -->
<!ENTITY sdot     CDATA "&#8901;" -- dot operator, U+22C5 ISOamsb -->
<!-- dot operator is NOT the same character as U+00B7 middle dot -->

<!-- Miscellaneous Technical -->
<!ENTITY lceil    CDATA "&#8968;" -- left ceiling = apl upstile,
                                     U+2308 ISOamsc  -->
<!ENTITY rceil    CDATA "&#8969;" -- right ceiling, U+2309 ISOamsc  -->
<!ENTITY lfloor   CDATA "&#8970;" -- left floor = apl downstile,
                                     U+230A ISOamsc  -->
<!ENTITY rfloor   CDATA "&#8971;" -- right floor, U+230B ISOamsc  -->
<!ENTITY lang     CDATA "&#9001;" -- left-pointing angle bracket = bra,
                                     U+2329 ISOtech -->
<!-- lang is NOT the same character as U+003C 'less than'
     or U+2039 'single left-pointing angle quotation mark' -->
<!ENTITY rang     CDATA "&#9002;" -- right-pointing angle bracket = ket,
                                     U+232A ISOtech -->
<!-- rang is NOT the same character as U+003E 'greater than'
     or U+203A 'single right-pointing angle quotation mark' -->

<!-- Geometric Shapes -->
<!ENTITY loz      CDATA "&#9674;" -- lozenge, U+25CA ISOpub -->

<!-- Miscellaneous Symbols -->
<!ENTITY spades   CDATA "&#9824;" -- black spade suit, U+2660 ISOpub -->
<!-- black here seems to mean filled as opposed to hollow -->
<!ENTITY clubs    CDATA "&#9827;" -- black club suit = shamrock,
                                     U+2663 ISOpub -->
<!ENTITY hearts   CDATA "&#9829;" -- black heart suit = valentine,
                                     U+2665 ISOpub -->
<!ENTITY diams    CDATA "&#9830;" -- black diamond suit, U+2666 ISOpub -->

24.4 Character entity references for markup-significant and
internationalization characters

The character entity references in this section are for escaping
markup-significant characters (these are the same as those in HTML 2.0 and
3.2), for denoting spaces and dashes. Other characters in this section apply
to internationalization issues such as the disambiguation of bidirectional
text (see the section on bidirectional text for details).

Entities have also been added for the remaining characters occurring in
CP-1252 which do not occur in the HTMLlat1 or HTMLsymbol entity sets. These
all occur in the 128 to 159 range within the cp-1252 charset. These entities
permit the characters to be denoted in a platform-independent manner.

To support these entities, user agents may support full [ISO10646] or use
other means. Display of glyphs for these characters may be obtained by being
able to display the relevant [ISO10646] characters or by other means, such
as internally mapping the listed entities, numeric character references, and
characters to the appropriate position in some font that contains the
requisite glyphs.

24.4.1 The list of characters

<!-- Special characters for HTML -->

<!-- Character entity set. Typical invocation:
     <!ENTITY % HTMLspecial PUBLIC
       "-//W3C//ENTITIES Special//EN//HTML">
     %HTMLspecial; -->

<!-- Portions © International Organization for Standardization 1986:
     Permission to copy in any form is granted for use with
     conforming SGML systems and applications as defined in
     ISO 8879, provided this notice is included in all copies.
-->

<!-- Relevant ISO entity set is given unless names are newly introduced.
     New names (i.e., not in ISO 8879 list) do not clash with any
     existing ISO 8879 entity names. ISO 10646 character numbers
     are given for each character, in hex. CDATA values are decimal
     conversions of the ISO 10646 values and refer to the document
     character set. Names are Unicode 2.0 names.

-->

<!-- C0 Controls and Basic Latin -->
<!ENTITY quot    CDATA "&#34;"   -- quotation mark = APL quote,
                                    U+0022 ISOnum -->
<!ENTITY amp     CDATA "&#38;"   -- ampersand, U+0026 ISOnum -->
<!ENTITY lt      CDATA "&#60;"   -- less-than sign, U+003C ISOnum -->
<!ENTITY gt      CDATA "&#62;"   -- greater-than sign, U+003E ISOnum -->

<!-- Latin Extended-A -->
<!ENTITY OElig   CDATA "&#338;"  -- latin capital ligature OE,
                                    U+0152 ISOlat2 -->
<!ENTITY oelig   CDATA "&#339;"  -- latin small ligature oe, U+0153 ISOlat2 -->
<!-- ligature is a misnomer, this is a separate character in some languages -->
<!ENTITY Scaron  CDATA "&#352;"  -- latin capital letter S with caron,
                                    U+0160 ISOlat2 -->
<!ENTITY scaron  CDATA "&#353;"  -- latin small letter s with caron,
                                    U+0161 ISOlat2 -->
<!ENTITY Yuml    CDATA "&#376;"  -- latin capital letter Y with diaeresis,
                                    U+0178 ISOlat2 -->

<!-- Spacing Modifier Letters -->
<!ENTITY circ    CDATA "&#710;"  -- modifier letter circumflex accent,
                                    U+02C6 ISOpub -->
<!ENTITY tilde   CDATA "&#732;"  -- small tilde, U+02DC ISOdia -->

<!-- General Punctuation -->
<!ENTITY ensp    CDATA "&#8194;" -- en space, U+2002 ISOpub -->
<!ENTITY emsp    CDATA "&#8195;" -- em space, U+2003 ISOpub -->
<!ENTITY thinsp  CDATA "&#8201;" -- thin space, U+2009 ISOpub -->
<!ENTITY zwnj    CDATA "&#8204;" -- zero width non-joiner,
                                    U+200C NEW RFC 2070 -->
<!ENTITY zwj     CDATA "&#8205;" -- zero width joiner, U+200D NEW RFC 2070 -->
<!ENTITY lrm     CDATA "&#8206;" -- left-to-right mark, U+200E NEW RFC 2070 -->
<!ENTITY rlm     CDATA "&#8207;" -- right-to-left mark, U+200F NEW RFC 2070 -->
<!ENTITY ndash   CDATA "&#8211;" -- en dash, U+2013 ISOpub -->
<!ENTITY mdash   CDATA "&#8212;" -- em dash, U+2014 ISOpub -->
<!ENTITY lsquo   CDATA "&#8216;" -- left single quotation mark,
                                    U+2018 ISOnum -->
<!ENTITY rsquo   CDATA "&#8217;" -- right single quotation mark,
                                    U+2019 ISOnum -->
<!ENTITY sbquo   CDATA "&#8218;" -- single low-9 quotation mark, U+201A NEW -->
<!ENTITY ldquo   CDATA "&#8220;" -- left double quotation mark,
                                    U+201C ISOnum -->
<!ENTITY rdquo   CDATA "&#8221;" -- right double quotation mark,
                                    U+201D ISOnum -->
<!ENTITY bdquo   CDATA "&#8222;" -- double low-9 quotation mark, U+201E NEW -->
<!ENTITY dagger  CDATA "&#8224;" -- dagger, U+2020 ISOpub -->
<!ENTITY Dagger  CDATA "&#8225;" -- double dagger, U+2021 ISOpub -->
<!ENTITY permil  CDATA "&#8240;" -- per mille sign, U+2030 ISOtech -->
<!ENTITY lsaquo  CDATA "&#8249;" -- single left-pointing angle quotation mark,
                                    U+2039 ISO proposed -->
<!-- lsaquo is proposed but not yet ISO standardized -->
<!ENTITY rsaquo  CDATA "&#8250;" -- single right-pointing angle quotation mark,
                                    U+203A ISO proposed -->
<!-- rsaquo is proposed but not yet ISO standardized -->
<!ENTITY euro   CDATA "&#8364;"  -- euro sign, U+20AC NEW -->

              Appendix A: Changes between HTML 3.2 and HTML 4.0

Contents

  1. Changes to elements
       1. New elements
       2. Deprecated elements
       3. Obsolete elements
  2. Changes to attributes
  3. Changes for accessibility
  4. Changes for meta data
  5. Changes for text
  6. Changes for links
  7. Changes for tables
  8. Changes for images, objects, and image maps
  9. Changes for forms
 10. Changes for style sheets
 11. Changes for frames
 12. Changes for scripting
 13. Changes for internationalization

A.1 Changes to elements

A.1.1 New elements

The new elements in HTML 4.0 are: ABBR, ACRONYM, BDO, BUTTON, COLGROUP, DEL,
FIELDSET, FRAME, FRAMESET, IFRAME, INS, LABEL, LEGEND, NOFRAMES, NOSCRIPT,
OBJECT, OPTGROUP, PARAM, SPAN, TBODY, TFOOT, THEAD, and Q.

A.1.2 Deprecated elements

The following elements are deprecated: APPLET, BASEFONT, CENTER, DIR, FONT,
ISINDEX, MENU, S, STRIKE, and U.

A.1.3 Obsolete elements

The following elements are obsolete: LISTING, PLAINTEXT, and XMP. For all of
them, authors should use the PRE element instead.

A.2 Changes to attributes

   * Almost all attributes that specify the presentation of an HTML document
     (e.g., colors, alignment, fonts, graphics, etc.) have been deprecated
     in favor of style sheets. The list of attributes in the appendix
     indicates which attributes have been deprecated.
   * The id and class attribute allow authors to assign name and class
     information to elements for style sheets, as anchors, for scripting,
     for object declarations, general purpose document processing, etc.

A.3 Changes for accessibility

HTML 4.0 features many changes to promote accessibility, including:

   * The title attribute may now be set on virtually every element.
   * Authors may provide long descriptions of tables, images, and frames
     (see the longdesc attribute).

A.4 Changes for meta data

Authors may now specify profiles that provide explanations about meta
specified with the META or LINK elements.

A.5 Changes for text

   * New features for internationalization allow authors to specify text
     direction and language.
   * The INS and DEL elements allow authors to mark up changes in their
     documents.
   * The ABBR and ACRONYM elements allow authors to mark up abbreviations
     and acronyms in their documents.

A.6 Changes for links

   * The id attribute makes any element the destination anchor of a link.

A.7 Changes for tables

The HTML 4.0 table model has grown out of early work on HTML+ and the
initial draft of HTML3.0. The earlier model has been extended in response to
requests from information providers as follows:

   * Authors may specify tables that may be incrementally displayed as the
     user agent receives data.
   * Authors may specify tables that are more accessible to users with
     non-visual user agents.
   * Authors may specify tables with fixed headers and footers. User agents
     may take advantage of these when scrolling large tables or rendering
     tables to paged media.

The HTML 4.0 table model also satisfies requests for optional column-based
defaults for alignment properties, more flexibility in specifying table
frames and rules, and the ability to align on designated characters. It is
expected, however, that style sheets will take over the task of rendering
tables in the near future.

In addition, a major goal has been to provide backwards compatibility with
the widely deployed Netscape implementation of tables. Another goal has been
to simplify importing tables conforming to the SGML CALS model. The latest
draft makes the align attribute compatible with the latest versions of the
most popular browsers. Some clarifications have been made to the role of the
dir attribute and recommended behavior when absolute and relative column
widths are mixed.

A new element, COLGROUP, has been introduced to allow sets of columns to be
grouped with different width and alignment properties specified by one or
more COL elements. The semantics of COLGROUP have been clarified over
previous drafts, and rules="basic" replaced by rules="groups".

The style attribute is included as a means for extending the properties
associated with edges and interiors of groups of cells. For instance, the
line style: dotted, double, thin/thick etc; the color/pattern fill for the
interior; cell margins and font information. This will be the subject for a
companion specification on style sheets.

The frame and rules attributes have been modified to avoid SGML name clashes
with each other, and to avoid clashes with the align and valign attributes.
These changes were additionally motivated by the desire to avoid future
problems if this specification is extended to allow frame and rules
attributes with other table elements.

A.8 Changes for images, objects, and image maps

   * The OBJECT element allows generic inclusion of objects.
   * The IFRAME and OBJECT elements allow authors to create embedded
     documents.
   * The alt attribute is required on the IMG and AREA elements.
   * The mechanism for creating image maps now allows authors to create more
     accessible image maps. The content model of the MAP element has changed
     for this reason.

A.9 Changes for forms

This specification introduces several new attributes and elements that
affect forms:

   * The accesskey attribute allows authors to specify direct keyboard
     access to form controls.
   * The disabled attribute allows authors to make a form control initially
     insensitive.
   * The readonly, allows authors to prohibit changes to a form control.
   * The LABEL element associates a label with a particular form control.
   * The FIELDSET element groups related fields together and, in association
     with the LEGEND element, can be used to name the group. Both of these
     new elements allow better rendering and better interactivity.
     Speech-based browsers can better describe the form and graphic browsers
     can make labels sensitive.
   * A new set of attributes, in combination with scripts, allow form
     providers to verify user-entered data.
   * The BUTTON element and INPUT with type set to "button" can be used in
     combination with scripts to create richer forms.
   * The OPTGROUP element allows authors to group menu options together in a
     SELECT, which is particularly important for form accessibility.
   * Additional changes for internationalization.

A.10 Changes for style sheets

HTML 4.0 supports a larger set of media descriptors so that authors may
write device-sensitive style sheets.

A.11 Changes for frames

HTML 4.0 supports frame documents and inline frames.

A.12 Changes for scripting

Many elements now feature event attributes that may be coupled with scripts;
the script is executed when the event occurs (e.g., when a document is
loaded, when the mouse is clicked, etc.).

A.13 Changes for internationalization

HTML 4.0 integrates the recommendations of [RFC2070] for the
internationalization of HTML.

However, this specification and [RFC2070] differ as follows:

   * The accept-charset attribute has been specified for the FORM element
     rather than the TEXTAREA and INPUT elements.
   * The HTML 4.0 specification makes additional clarifications with respect
     to the bidirectional algorithm.
   * The use of CDATA to define the SCRIPT and STYLE elements does not
     preserve the ability to transcode documents, as described in section
     2.1 of [RFC2070].

          Appendix B: Performance, Implementation, and Design Notes

Contents

  1. Notes on invalid documents
  2. Special characters in URI attribute values
       1. Non-ASCII characters in URI attribute values
       2. Ampersands in URI attribute values
  3. SGML implementation notes
       1. Line breaks
       2. Specifying non-HTML data
             + Element content
             + Attribute values
       3. SGML features with limited support
       4. Boolean attributes
       5. Marked Sections
       6. Processing Instructions
       7. Shorthand markup
  4. Notes on helping search engines index your Web site
       1. Search robots
             + The robots.txt file
             + Robots and the META element
  5. Notes on tables
       1. Design rationale
             + Dynamic reformatting
             + Incremental display
             + Structure and presentation
             + Row and column groups
             + Accessibility
       2. Recommended Layout Algorithms
             + Fixed Layout Algorithm
             + Autolayout Algorithm
  6. Notes on forms
       1. Incremental display
       2. Future projects
  7. Notes on scripting
       1. Reserved syntax for future script macros
             + Current Practice for Script Macros
  8. Notes on frames
  9. Notes on accessibility
 10. Notes on security
       1. Security issues for forms

The following notes are informative, not normative. Despite the appearance
of words such as "must" and "should", all requirements in this section
appear elsewhere in the specification.

B.1 Notes on invalid documents

This specification does not define how conforming user agents handle general
error conditions, including how user agents behave when they encounter
elements, attributes, attribute values, or entities not specified in this
document.

However, to facilitate experimentation and interoperability between
implementations of various versions of HTML, we recommend the following
behavior:

   * If a user agent encounters an element it does not recognize, it should
     try to render the element's content.
   * If a user agent encounters an attribute it does not recognize, it
     should ignore the entire attribute specification (i.e., the attribute
     and its value).
   * If a user agent encounters an attribute value it doesn't recognize, it
     should use the default attribute value.
   * If it encounters an undeclared entity, the entity should be treated as
     character data.

We also recommend that user agents provide support for notifying the user of
such errors.

Since user agents may vary in how they handle error conditions, authors and
users must not rely on specific error recovery behavior.

The HTML 2.0 specification ([RFC1866]) observes that many HTML 2.0 user
agents assume that a document that does not begin with a document type
declaration refers to the HTML 2.0 specification. As experience shows that
this is a poor assumption, the current specification does not recommend this
behavior.

For reasons of interoperability, authors must not "extend" HTML through the
available SGML mechanisms (e.g., extending the DTD, adding a new set of
entity definitions, etc.).

B.2 Special characters in URI attribute values

B.2.1 Non-ASCII characters in URI attribute values

Although URIs do not contain non-ASCII values (see [URI], section 2.1)
authors sometimes specify them in attribute values expecting URIs (i.e.,
defined with %URI; in the DTD). For instance, the following href value is
illegal:

<A href="http://foo.org/Håkon">...</A>

We recommend that user agents adopt the following convention for handling
non-ASCII characters in such cases:

  1. Represent each character in UTF-8 (see [RFC2044]) as one or more bytes.
  2. Escape these bytes with the URI escaping mechanism (i.e., by converting
     each byte to %HH, where HH is the hexadecimal notation of the byte
     value).

This procedure results in a syntactically legal URI (as defined in
[RFC1738], section 2.2 or [RFC2141], section 2) that is independent of the
character encoding to which the HTML document carrying the URI may have been
transcoded.

Note. Some older user agents trivially process URIs in HTML using the bytes
of the character encoding in which the document was received. Some older
HTML documents rely on this practice and break when transcoded. User agents
that want to handle these older documents should, on receiving a URI
containing characters outside the legal set, first use the conversion based
on UTF-8. Only if the resulting URI does not resolve should they try
constructing a URI based on the bytes of the character encoding in which the
document was received.

Note. The same conversion based on UTF-8 should be applied to values of the
name attribute for the A element.

B.2.2 Ampersands in URI attribute values

The URI that is constructed when a form is submitted may be used as an
anchor-style link (e.g., the href attribute for the A element).
Unfortunately, the use of the "&" character to separate form fields
interacts with its use in SGML attribute values to delimit character entity
references. For example, to use the URI "http://host/?x=1&y=2" as a linking
URI, it must be written <A href="http://host/?x=1&#38;y=2"> or <A
href="http://host/?x=1&amp;y=2">.

We recommend that HTTP server implementors, and in particular, CGI
implementors support the use of ";" in place of "&" to save authors the
trouble of escaping "&" characters in this manner.

B.3 SGML implementation notes

B.3.1 Line breaks

SGML (see [ISO8879], section 7.6.1) specifies that a line break immediately
following a start tag must be ignored, as must a line break immediately
before an end tag. This applies to all HTML elements without exception.

The following two HTML examples must be rendered identically:

<P>Thomas is watching TV.</P>

<P>
Thomas is watching TV.
</P>

So must the following two examples:

<A>My favorite Website</A>

<A>
My favorite Website
</A>

B.3.2 Specifying non-HTML data

Script and style data may appear as element content or attribute values. The
following sections describe the boundary between HTML markup and foreign
data.

Note.The DTD defines script and style data to be CDATA for both element
content and attribute values. SGML rules do not allow character references
in CDATA element content but do allow them in CDATA attribute values.
Authors should pay particular attention when cutting and pasting script and
style data between element content and attribute values.

This asymmetry also means that when transcoding from a richer to a poorer
character encoding, the transcoder cannot simply replace unconvertible
characters in script or style data with the corresponding numeric character
references; it must parse the HTML document and know about each script and
style language's syntax in order to process the data correctly.

Element content

When script or style data is the content of an element (SCRIPT and STYLE),
the data begins immediately after the element start tag and ends at the
first ETAGO ("</") delimiter followed by a name character ([a-zA-Z]); note
that this may not be the element's end tag. Authors should therefore escape
sequences "</" sequence within the content. Escape mechanisms are specific
to each scripting or style sheet language.

ILLEGAL EXAMPLE:
The following script data incorrectly contains a "</" sequence (as part of
"</EM>") before the SCRIPT end tag:

    <SCRIPT type="text/javascript">
      document.write ("<EM>This won't work</EM>")
    </SCRIPT>

In JavaScript, this code can be expressed legally by hiding the ETAGO
delimiter before an SGML name start character:

    <SCRIPT type="text/javascript">
      document.write ("<EM>This will work<\/EM>")
    </SCRIPT>

In Tcl, one may accomplish this as follows:

    <SCRIPT type="text/tcl">
      document write "<EM>This will work<\/EM>"
    </SCRIPT>

In VBScript, the problem may be avoided with the Chr() function:

    "<EM>This will work<" & Chr(47) & "EM>"

Attribute values

When script or style data is the value of an attribute (either style or the
intrinsic event attributes), authors should escape occurrences of the
delimiting single or double quotation mark within the value according to the
script or style language convention. Authors should also escape occurrences
of "&" if the "&" is not meant to be the beginning of a character reference.

   * '"' should be written as "&quot;" or "&#34;"
   * '&' should be written as "&amp;" or "&#38;"

Thus, for example, one could write:

 <INPUT name="num" value="0"
 onchange="if (compare(this.value, &quot;help&quot;)) {gethelp()}">

B.3.3 SGML features with limited support

SGML systems conforming to [ISO8879] are expected to recognize a number of
features that aren't widely supported by HTML user agents. We recommend that
authors avoid using all of these features.

B.3.4 Boolean attributes

Authors should be aware than many user agents only recognize the minimized
form of boolean attributes and not the full form.

For instance, authors may want to specify:

<OPTION selected>

instead of

<OPTION selected="selected">

B.3.5 Marked Sections

Marked sections play a role similar to the #ifdef construct recognized by C
preprocessors.

<![INCLUDE[
 <!-- this will be included -->
]]>

<![IGNORE[
 <!-- this will be ignored -->
]]>

SGML also defines the use of marked sections for CDATA content, within which
"<" is not treated as the start of a tag, e.g.,

<![CDATA[
 <an> example of <sgml> markup that is
 not <painful> to write with < and such.
]]>

The telltale sign that a user agent doesn't recognize a marked section is
the appearance of "]]>", which is seen when the user agent mistakenly uses
the first ">" character as the end of the tag starting with "<![".

B.3.6 Processing Instructions

Processing instructions are a mechanism to capture platform-specific idioms.
A processing instruction begins with <? and ends with >

<?instruction >

For example:

<?>
<?style tt = font courier>
<?page break>
<?experiment> ... <?/experiment>

Authors should be aware that many user agents render processing instructions
as part of the document's text.

B.3.7 Shorthand markup

Some SGML SHORTTAG constructs save typing but add no expressive capability
to the SGML application. Although these constructs technically introduce no
ambiguity, they reduce the robustness of documents, especially when the
language is enhanced to include new elements. Thus, while SHORTTAG
constructs of SGML related to attributes are widely used and implemented,
those related to elements are not. Documents that use them are conforming
SGML documents, but are unlikely to work with many existing HTML tools.

The SHORTTAG constructs in question are the following:

   * NET tags:

     <name/.../

   * closed Start Tag:

     <name1<name2>

   * Empty Start Tag:

     <>

   * Empty End Tag:

     </>

B.4 Notes on helping search engines index your Web site

This section provides some simple suggestions that will make your documents
more accessible to search engines.

Define the document language
     In the global context of the Web it is important to know which human
     language a page was written in. This is discussed in the section on
     language information.
Specify language variants of this document
     If you have prepared translations of this document into other
     languages, you should use the LINK element to reference these. This
     allows an indexing engine to offer users search results in the user's
     preferred language, regardless of how the query was written. For
     instance, the following links offer French and German alternatives to a
     search engine:

     <LINK rel="alternate"
              type="text/html"
              href="mydoc-fr.html" hreflang="fr"
              lang="fr" title="La vie souterraine">
     <LINK rel="alternate"
              type="text/html"
              href="mydoc-de.html" hreflang="de"
              lang="de" title="Das Leben im Untergrund">

Provide keywords and descriptions
     Some indexing engines look for META elements that define a
     comma-separated list of keywords/phrases, or that give a short
     description. Search engines may present these keywords as the result of
     a search. The value of the name attribute sought by a search attribute
     is not defined by this specification. Consider these examples,

     <META name="keywords" content="vacation,Greece,sunshine">
     <META name="description" content="Idyllic European vacations">

Indicate the beginning of a collection
     Collections of word processing documents or presentations are
     frequently translated into collections of HTML documents. It is helpful
     for search results to reference the beginning of the collection in
     addition to the page hit by the search. You may help search engines by
     using the LINK element with rel="begin" along with a TITLE, as in:


     <LINK rel="begin"
              type="text/html"
              href="page1.html"
              title="General Theory of Relativity">

Provide robots with indexing instructions
     People may be surprised to find that their site has been indexed by an
     indexing robot and that the robot should not have been permitted to
     visit a sensitive part of the site. Many Web robots offer facilities
     for Web site administrators and content providers to limit what the
     robot does. This is achieved through two mechanisms: a "robots.txt"
     file and the META element in HTML documents, described below.

B.4.1 Search robots

The robots.txt file

When a Robot visits a Web site, say http://www.foobar.com/, it firsts checks
for http://www.foobar.com/robots.txt. If it can find this document, it will
analyze its contents to see if it is allowed to retrieve the document. You
can customize the robots.txt file to apply only to specific robots, and to
disallow access to specific directories or files.

Here is a sample robots.txt file that prevents all robots from visiting the
entire site

        User-agent: *    # applies to all robots
        Disallow: /      # disallow indexing of all pages

The Robot will simply look for a "/robots.txt" URI on your site, where a
site is defined as a HTTP server running on a particular host and port
number. Here are some sample locations for robots.txt:

                Site URI                  URI for robots.txt

        http://www.w3.org/        http://www.w3.org/robots.txt

        http://www.w3.org:80/     http://www.w3.org:80/robots.txt

        http://www.w3.org:1234/   http://www.w3.org:1234/robots.txt

        http://w3.org/            http://w3.org/robots.txt

There can only be a single "/robots.txt" on a site. Specifically, you should
not put "robots.txt" files in user directories, because a robot will never
look at them. If you want your users to be able to create their own
"robots.txt", you will need to merge them all into a single "/robots.txt".
If you don't want to do this your users might want to use the Robots META
Tag instead.

Some tips: URI's are case-sensitive, and "/robots.txt" string must be all
lower-case. Blank lines are not permitted.

There must be exactly one "User-agent" field per record. The robot should be
liberal in interpreting this field. A case-insensitive substring match of
the name without version information is recommended.

If the value is "*", the record describes the default access policy for any
robot that has not matched any of the other records. It is not allowed to
have multiple such records in the "/robots.txt" file.

The "Disallow" field specifies a partial URI that is not to be visited. This
can be a full path, or a partial path; any URI that starts with this value
will not be retrieved. For example,

    Disallow: /help disallows both /help.html and /help/index.html, whereas
    Disallow: /help/ would disallow /help/index.html but allow /help.html.

An empty value for "Disallow", indicates that all URIs can be retrieved. At
least one "Disallow" field must be present in the robots.txt file.

Robots and the META element

The META element allows HTML authors to tell visiting robots whether a
document may be indexed, or used to harvest more links. No server
administrator action is required.

In the following example a robot should neither index this document, nor
analyze it for links.

<META name="ROBOTS" content="NOINDEX, NOFOLLOW">

The list of terms in the content is ALL, INDEX, NOFOLLOW, NOINDEX. The name
and the content attribute values are case-insensitive.

Note. In early 1997 only a few robots implement this, but this is expected
to change as more public attention is given to controlling indexing robots.

B.5 Notes on tables

B.5.1 Design rationale

The HTML table model has evolved from studies of existing SGML tables
models, the treatment of tables in common word processing packages, and a
wide range of tabular layout techniques in magazines, books and other
paper-based documents. The model was chosen to allow simple tables to be
expressed simply with extra complexity available when needed. This makes it
practical to create the markup for HTML tables with everyday text editors
and reduces the learning curve for getting started. This feature has been
very important to the success of HTML to date.

Increasingly, people are creating tables by converting from other document
formats or by creating them directly with WYSIWYG editors. It is important
that the HTML table model fit well with these authoring tools. This affects
how the cells that span multiple rows or columns are represented, and how
alignment and other presentation properties are associated with groups of
cells.

Dynamic reformatting

A major consideration for the HTML table model is that the author does not
control how a user will size a table, what fonts he or she will use, etc.
This makes it risky to rely on column widths specified in terms of absolute
pixel units. Instead, tables must be able to change sizes dynamically to
match the current window size and fonts. Authors can provide guidance as to
the relative widths of columns, but user agents should ensure that columns
are wide enough to render the width of the largest element of the cell's
content. If the author's specification must be overridden, relative widths
of individual columns should not be changed drastically.

Incremental display

For large tables or slow network connections, incremental table display is
important to user satisfaction. User agents should be able to begin
displaying a table before all of the data has been received. The default
window width for most user agents shows about 80 characters, and the
graphics for many HTML pages are designed with these defaults in mind. By
specifying the number of columns, and including provision for control of
table width and the widths of different columns, authors can give hints to
user agents that allow the incremental display of table contents.

For incremental display, the browser needs the number of columns and their
widths. The default width of the table is the current window size
(width="100%"). This can be altered by setting the width-TABLE attribute of
the TABLE element. By default, all columns have the same width, but you can
specify column widths with one or more COL elements before the table data
starts.

The remaining issue is the number of columns. Some people have suggested
waiting until the first row of the table has been received, but this could
take a long time if the cells have a lot of content. On the whole it makes
more sense, when incremental display is desired, to get authors to
explicitly specify the number of columns in the TABLE element.

Authors still need a way of telling user agents whether to use incremental
display or to size the table automatically to fit the cell contents. In the
two pass auto-sizing mode, the number of columns is determined by the first
pass. In the incremental mode, the number of columns must be stated up
front. It makes more sense to set the cols attribute to the number of
columns rather than using some "layout" attribute (e.g., layout="fixed" or
layout="auto").

Structure and presentation

HTML distinguishes structural markup such as paragraphs and quotations from
rendering idioms such as margins, fonts, colors, etc. How does this
distinction affect tables? From the purist's point of view, the alignment of
text within table cells and the borders between cells is a rendering issue,
not one of structure. In practice, though, it is useful to group these with
the structural information, as these features are highly portable from one
application to the next. The HTML table model leaves most rendering
information to associated style sheets. The model presented in this
specification is designed to take advantage of such style sheets but not to
require them.

Current desktop publishing packages provide very rich control over the
rendering of tables, and it would be impractical to reproduce this in HTML,
without making HTML into a bulky rich text format like RTF or MIF. This
specification does, however, offer authors the ability to choose from a set
of commonly used classes of border styles. The frame attribute controls the
appearance of the border frame around the table while the rules attribute
determines the choice of rulings within the table. A finer level of control
will be supported via rendering annotations. The style attribute can be used
for specifying rendering information for individual elements. Further
rendering information can be given with the STYLE element in the document
head or via linked style sheets.

During the development of this specification, a number of avenues were
investigated for specifying the ruling patterns for tables. One issue
concerns the kinds of statements that can be made. Including support for
edge subtraction as well as edge addition leads to relatively complex
algorithms. For instance, work on allowing the full set of table elements to
include the frame and rules attributes led to an algorithm involving some 24
steps to determine whether a particular edge of a cell should be ruled or
not. Even this additional complexity doesn't provide enough rendering
control to meet the full range of needs for tables. The current
specification deliberately sticks to a simple intuitive model, sufficient
for most purposes. Further experimental work is needed before a more complex
approach is standardized.

Row and column groups

This specification provides a superset of the simpler model presented in
earlier work on HTML+. Tables are considered as being formed from an
optional caption together with a sequence of rows, which in turn consist of
a sequence of table cells. The model further differentiates header and data
cells, and allows cells to span multiple rows and columns.

Following the CALS table model (see [CALS]), this specification allows table
rows to be grouped into head and body and foot sections. This simplifies the
representation of rendering information and can be used to repeat table head
and foot rows when breaking tables across page boundaries, or to provide
fixed headers above a scrollable body panel. In the markup, the foot section
is placed before the body sections. This is an optimization shared with CALS
for dealing with very long tables. It allows the foot to be rendered without
having to wait for the entire table to be processed.

Accessibility

For the visually impaired, HTML offers the hope of setting to rights the
damage caused by the adoption of windows based graphical user interfaces.
The HTML table model includes attributes for labeling each cell, to support
high quality text to speech conversion. The same attributes can also be used
to support automated import and export of table data to databases or
spreadsheets.

B.5.2 Recommended Layout Algorithms

If the cols attribute on the TABLE element specifies the number of columns,
then the table may be rendered using a fixed layout, otherwise the
autolayout algorithm described below should be used.

If the width attribute is not specified, visual user agents should assume a
default value of 100% for formatting.

It is recommended that user agents increase table widths beyond the value
specified by width in cases when cell contents would otherwise overflow.
User agents that override the specified width should do so within reason.
User agents may elect to split words across lines to avoid the need for
excessive horizontal scrolling or when such scrolling is impractical or
undesired.

For the purposes of layout, user agents should consider that table captions
(specified by the CAPTION element) behave like cells. Each caption is a cell
that spans all of the table's columns if at the top or bottom of the table,
and rows if at the left or right side of the table.

Fixed Layout Algorithm

For this algorithm, it is assumed that the number of columns is known. The
column widths by default should be set to the same size. Authors may
override this by specifying relative or absolute column widths, using the
COLGROUP or COL elements. The default table width is the space between the
current left and right margins, but may be overridden by the width attribute
on the TABLE element, or determined from absolute column widths. To deal
with mixtures of absolute and relative column widths, the first step is to
allocate space from the table width to columns with absolute widths. After
this, the space remaining is divided up between the columns with relative
widths.

The table syntax alone is insufficient to guarantee the consistency of
attribute values. For instance, the number of columns specified by the cols
attribute may be inconsistent with the number of columns implied by the COL
elements. This in turn, may be inconsistent with the number of columns
implied by the table cells. A further problem occurs when the columns are
too narrow to avoid overflow of cell contents. The width of the table as
specified by the TABLE element or COL elements may result in overflow of
cell contents. It is recommended that user agents attempt to recover
gracefully from these situations, e.g., by hyphenating words and resorting
to splitting words if hyphenation points are unknown.

In the event that an indivisible element causes cell overflow, the user
agent may consider adjusting column widths and re-rendering the table. In
the worst case, clipping may be considered if column width adjustments
and/or scrollable cell content are not feasible. In any case, if cell
content is split or clipped this should be indicated to the user in an
appropriate manner.

Autolayout Algorithm

If the COLS attribute is missing from the table start tag, then the user
agent should use the following autolayout algorithm. It uses two passes
through the table data and scales linearly with the size of the table.

In the first pass, line wrapping is disabled, and the user agent keeps track
of the minimum and maximum width of each cell. The maximum width is given by
the widest line. Since line wrap has been disabled, paragraphs are treated
as long lines unless broken by BR elements. The minimum width is given by
the widest text element (word, image, etc.) taking into account leading
indents and list bullets, etc. In other words, it is necessary to determine
the minimum width a cell would require in a window of its own before the
cell begins to overflow. Allowing user agents to split words will minimize
the need for horizontal scrolling or in the worst case, clipping the cell
contents.

This process also applies to any nested tables occurring in cell content.
The minimum and maximum widths for cells in nested tables are used to
determine the minimum and maximum widths for these tables and hence for the
parent table cell itself. The algorithm is linear with aggregate cell
content, and broadly speaking, independent of the depth of nesting.

To cope with character alignment of cell contents, the algorithm keeps three
running min/max totals for each column: Left of align char, right of align
char and unaligned. The minimum width for a column is then: max(min_left +
min_right, min_non-aligned).

The minimum and maximum cell widths are then used to determine the
corresponding minimum and maximum widths for the columns. These in turn, are
used to find the minimum and maximum width for the table. Note that cells
can contain nested tables, but this doesn't complicate the code
significantly. The next step is to assign column widths according to the
available space (i.e., the space between the current left and right
margins).

For cells that span multiple columns, a simple approach consists of
apportioning the min/max widths evenly to each of the constituent columns. A
slightly more complex approach is to use the min/max widths of unspanned
cells to weight how spanned widths are apportioned. Experiments suggest that
a blend of the two approaches gives good results for a wide range of tables.

The table borders and intercell margins need to be included in assigning
column widths. There are three cases:

  1. The minimum table width is equal to or wider than the available space.
     In this case, assign the minimum widths and allow the user to scroll
     horizontally. For conversion to braille, it will be necessary to
     replace the cells by references to notes containing their full content.
     By convention these appear before the table.
  2. The maximum table width fits within the available space. In this case,
     set the columns to their maximum widths.
  3. The maximum width of the table is greater than the available space, but
     the minimum table width is smaller. In this case, find the difference
     between the available space and the minimum table width, lets call it
     W. Lets also call D the difference between maximum and minimum width of
     the table.

     For each column, let d be the difference between maximum and minimum
     width of that column. Now set the column's width to the minimum width
     plus d times W over D. This makes columns with large differences
     between minimum and maximum widths wider than columns with smaller
     differences.

This assignment step is then repeated for nested tables using the minimum
and maximum widths derived for all such tables in the first pass. In this
case, the width of the parent table cell plays the role of the current
window size in the above description. This process is repeated recursively
for all nested tables. The topmost table is then rendered using the assigned
widths. Nested tables are subsequently rendered as part of the parent
table's cell contents.

If the table width is specified with the width attribute, the user agent
attempts to set column widths to match. The width attribute is not binding
if this results in columns having less than their minimum (i.e.,
indivisible) widths.

If relative widths are specified with the COL element, the algorithm is
modified to increase column widths over the minimum width to meet the
relative width constraints. The COL elements should be taken as hints only,
so columns shouldn't be set to less than their minimum width. Similarly,
columns shouldn't be made so wide that the table stretches well beyond the
extent of the window. If a COL element specifies a relative width of zero,
the column should always be set to its minimum width.

When using the two pass layout algorithm, the default alignment position in
the absence of an explicit or inherited charoff attribute can be determined
by choosing the position that would center lines for which the widths before
and after the alignment character are at the maximum values for any of the
lines in the column for which align="char". For incremental table layout the
suggested default is charoff="50%". If several cells in different rows for
the same column use character alignment, then by default, all such cells
should line up, regardless of which character is used for alignment. Rules
for handling objects too large for column apply when the explicit or implied
alignment results in a situation where the data exceeds the assigned width
of the column.

Choice of attribute names. It would have been preferable to choose values
for the frame attribute consistent with the rules attribute and the values
used for alignment. For instance: none, top, bottom, topbot, left, right,
leftright, all. Unfortunately, SGML requires enumerated attribute values to
be unique for each element, independent of the attribute name. This causes
immediate problems for "none", "left", "right" and "all". The values for
theframe attribute have been chosen to avoid clashes with the rules, align
and valign-COLGROUP attributes. This provides a measure of future proofing,
as it is anticipated that the frame and rules attributes will be added to
other table elements in future revisions to this specification. An
alternative would be to make frame a CDATA attribute. The consensus of the
W3C HTML Working Group was that the benefits of being able to use SGML
validation tools to check attributes based on enumerated values outweighs
the need for consistent names.

B.6 Notes on forms

B.6.1 Incremental display

The incremental display of documents being received from the network gives
rise to certain problems with respect to forms. User agents should prevent
forms from being submitted until all of the form's elements have been
received.

The incremental display of documents raises some issues with respect to
tabbing navigation. The heuristic of giving focus to the lowest valued
tabindex in the document seems reasonable enough at first glance. However
this implies having to wait until all of the document's text is received,
since until then, the lowest valued tabindex may still change. If the user
hits the tab key before then, it is reasonable for user agents to move the
focus to the lowest currently available tabindex.

If forms are associated with client-side scripts, there is further potential
for problems. For instance, a script handler for a given field may refer to
a field that doesn't yet exist.

B.6.2 Future projects

This specification defines a set of elements and attributes powerful enough
to fulfill the general need for producing forms. However there is still room
for many possible improvements. For instance the following problems could be
addressed in the future:

   * The range of form field types is too limited in comparison with modern
     user interfaces. For instance there is no provision for tabular data
     entry, sliders or multiple page layouts.
   * Servers cannot update the fields in a submitted form and instead have
     to send a complete HTML document causing screen flicker.
   * These also cause problems for speech based browsers, making it
     difficult for the visually impaired to interact with HTML forms.

Another possible extension would be to add the usemap attribute to INPUT for
use as client-side image map when "type=image". The AREA element
corresponding to the location clicked would contribute the value to be
passed to the server. To avoid the need to modify server scripts, it may be
appropriate to extend AREA to provide x and y values for use with the INPUT
element.

B.7 Notes on scripting

B.7.1 Reserved syntax for future script macros

This specification reserves syntax for the future support of script macros
in HTML CDATA attributes. The intention is to allow attributes to be set
depending on the properties of objects that appear earlier on the page. The
syntax is:

   attribute = "... &{ macro body }; ... "

Current Practice for Script Macros

The macro body is made up of one or more statements in the default scripting
language (as per intrinsic event attributes). The semicolon following the
right brace is always needed, as otherwise the right brace character "}" is
treated as being part of the macro body. Its also worth noting that quote
marks are always needed for attributes containing script macros.

The processing of CDATA attributes proceeds as follows:

  1. The SGML parser evaluates any SGML entities (e.g., "&gt;").
  2. Next the script macros are evaluated by the script engine.
  3. Finally the resultant character string is passed to the application for
     subsequent processing.

Macro processing takes place when the document is loaded (or reloaded) but
does not take place again when the document is resized, repainted, etc.

DEPRECATED EXAMPLE:
Here are some examples using JavaScript. The first one randomizes the
document background color:


<BODY bgcolor='&{randomrbg};'>

Perhaps you want to dim the background for evening viewing:


<BODY bgcolor='&{if(Date.getHours > 18)...};'>

The next example uses JavaScript to set the coordinates for a client-side
image map:


<MAP NAME=foo>
   <AREA shape="rect" coords="&{myrect(imageuri)};" href="&{myuri};" alt="">
 </MAP>

This example sets the size of an image based upon document properties:


<IMG src="bar.gif" width='&{document.banner.width/2};' height='50%' alt="banner">

You can set the URI for a link or image by script:

 <SCRIPT type="text/javascript">
   function manufacturer(widget) {
       ...
   }
   function location(manufacturer) {
       ...
   }
   function logo(manufacturer) {
       ...
   }
 </SCRIPT>
  <A href='&{location(manufacturer("widget"))};'>widget</A>
  <IMG src='&{logo(manufacturer("widget"))};' alt="logo">

This last example shows how SGML CDATA attributes can be quoted using single
or double quote marks. If you use single quotes around the attribute string
then you can include double quote marks as part of the attribute string.
Another approach is use &quot; for double quote marks:


<IMG src="&{logo(manufacturer(&quot;widget&quot;))};" alt="logo">

B.8 Notes on frames

Since there is no guarantee that a frame target name is unique, it is
appropriate to describe the current practice in finding a frame given a
target name:

  1. If the target name is a reserved word as described in the normative
     text, apply it as described.
  2. Otherwise, perform a depth-first search of the frame hierarchy in the
     window that contained the link. Use the first frame whose name is an
     exact match.
  3. If no such frame was found in (2), apply step 2 to each window, in a
     front-to-back ordering. Stop as soon as you encounter a frame with
     exactly the same name.
  4. If no such frame was found in (3), create a new window and assign it
     the target name.

B.9 Notes on accessibility

Note. The following algorithm for generating alternate text may be
superseded by recommendations by the W3C Web Accessibility Initiative Group.
Please consult [WAIGUIDE] for more information.

When an author does not set the alt attribute for the IMG or APPLET
elements, user agents should supply the alternate text, calculated in the
following order:

  1. If the title has been specified, its value should be used as alternate
     text.
  2. Otherwise, if HTTP headers provide title information when the included
     object is retrieved, this information should be used as alternate text.
  3. Otherwise, if the included object contains text fields (e.g., GIF
     images contain some text fields), information extracted from the text
     fields should be used as alternate text. Since user agents may have to
     retrieve an entire object first in order to extract textual
     information, user agents may adopt more economical approaches (e.g.,
     content negotiation).
  4. Otherwise, in the absence of other information, user agents should use
     the file name (minus the extension) as alternate text.

When an author does not set the alt attribute for the INPUT element, user
agents should supply the alternate text, calculated in the following order:

  1. If the title has been specified, its value should be used as alternate
     text.
  2. Otherwise, if the name has been specified, its value should be used as
     alternate text.
  3. Otherwise (submit and reset buttons), the value of the type attribute
     should be used as alternate text.

B.10 Notes on security

Anchors, embedded images, and all other elements that contain URIs as
parameters may cause the URI to be dereferenced in response to user input.
In this case, the security issues of [RFC1738], section 6, should be
considered. The widely deployed methods for submitting form requests -- HTTP
and SMTP -- provide little assurance of confidentiality. Information
providers who request sensitive information via forms -- especially with the
INPUT element, type="password" -- should be aware and make their users aware
of the lack of confidentiality.

B.10.1 Security issues for forms

A user agent should not send any file that the user has not explicitly asked
to be sent. Thus, HTML user agents are expected to confirm any default file
names that might be suggested by the value attribute of the INPUT element.
Hidden controls must not specify files.

This specification does not contain a mechanism for encryption of the data;
this should be handled by whatever other mechanisms are in place for secure
transmission of data.

Once a file is uploaded, the processing agent should process and store the
it appropriately.

                                 References

Contents

  1. Normative references
  2. Informative references

Normative references

[CSS1]
     "Cascading Style Sheets, level 1", H. W. Lie and B. Bos, 17 December
     1996.
     Available at http://www.w3.org/TR/REC-CSS1-961217
[DATETIME]
     "Date and Time Formats", W3C Note, M. Wolf and C. Wicksteed, 15
     September 1997.
     Available at http://www.w3.org/TR/NOTE-datetime
[IANA]
     "Assigned Numbers", STD 2, RFC 1700, USC/ISI, J. Reynolds and J.
     Postel, October 1994.
     Available at http://ds.internic.net/rfc/rfc1700.txt
[ISO639]
     "Codes for the representation of names of languages", ISO 639:1988.
     For more information, consult http://www.iso.ch/cate/d4766.html.
     See also http://www.sil.org/sgml/iso639a.html.
[ISO3166]
     "Codes for the representation of names of countries", ISO 3166:1993.
[ISO8601]
     "Data elements and interchange formats -- Information interchange --
     Representation of dates and times", ISO 8601:1988.
[ISO8879]
     "Information Processing -- Text and Office Systems -- Standard
     Generalized Markup Language (SGML)", ISO 8879:1986.
     Please consult http://www.iso.ch/cate/d16387.html for information about
     the standard.
[ISO10646]
     "Information Technology -- Universal Multiple-Octet Coded Character Set
     (UCS) -- Part 1: Architecture and Basic Multilingual Plane", ISO/IEC
     10646-1:1993. The current specification also takes into consideration
     the first five amendments to ISO/IEC 10646-1:1993.
[ISO88591]
     "Information Processing -- 8-bit single-byte coded graphic character
     sets -- Part 1: Latin alphabet No. 1", ISO 8859-1:1987.
[MIMETYPES]
     List of registered content types (MIME types). Download a list of
     registered content types from
     ftp://ftp.isi.edu/in-notes/iana/assignments/media-types/.
[RFC1555]
     "Hebrew Character Encoding for Internet Messages", H. Nussbacher and Y.
     Bourvine, December 1993.
     Available at http://ds.internic.net/rfc/rfc1555.txt.
[RFC1556]
     "Handling of Bi-directional Texts in MIME", H. Nussbacher, December
     1993.
     Available at http://ds.internic.net/rfc/rfc1556.txt.
[RFC1738]
     "Uniform Resource Locators", T. Berners-Lee, L. Masinter, and M.
     McCahill, December 1994.
     Available at http://ds.internic.net/rfc/rfc1738.txt.
[RFC1766]
     "Tags for the Identification of Languages", H. Alvestrand, March 1995.
     Available at http://ds.internic.net/rfc/rfc1766.txt.
[RFC1808]
     "Relative Uniform Resource Locators", R. Fielding, June 1995.
     Available at http://ds.internic.net/rfc/rfc1808.txt.
[RFC2044]
     "UTF-8, a transformation format of Unicode and ISO 10646", F. Yergeau,
     October 1996.
     Available at http://ds.internic.net/rfc/rfc2044.txt.
[RFC2045]
     "Multipurpose Internet Mail Extensions (MIME) Part One: Format of
     Internet Message Bodies", N. Freed and N. Borenstein, November 1996.
     Available at http://ds.internic.net/rfc/rfc2045.txt. Note that this RFC
     obsoletes RFC1521, RFC1522, and RFC1590.
[RFC2046]
     "Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types",
     N. Freed and N. Borenstein, November 1996.
     Available at http://ds.internic.net/rfc/rfc2046.txt. Note that this RFC
     obsoletes RFC1521, RFC1522, and RFC1590.
[RFC2068]
     "HTTP Version 1.1 ", R. Fielding, J. Gettys, J. Mogul, H. Frystyk
     Nielsen, and T. Berners-Lee, January 1997.
     Available at http://ds.internic. net/rfc/rfc2068.txt.
[RFC2119]
     "Key words for use in RFCs to Indicate Requirement Levels", S. Bradner,
     March 1997.
     Available at http://ds.internic.net/rfc/rfc2119.txt.
[RFC2141]
     "URN Syntax", R. Moats, May 1997.
     Available at http://ds.internic.net/rfc/rfc2141.txt.
[SRGB]
     "A Standard Default color Space for the Internet", version 1.10, M.
     Stokes, M. Anderson, S. Chandrasekar, and R. Motta, 5 November 1996.
     Available at http://www.w3.org/Graphics/Color/sRGB
[UNICODE]
     "The Unicode Standard: Version 2.0", The Unicode Consortium,
     Addison-Wesley Developers Press, 1996. The specification also takes
     into consideration the corrigenda at
     http://www.unicode.org/unicode/uni2errata/bidi.htm.
     For more information, consult the Unicode Consortium's home page at
     http://www.unicode.org/
[URI]
     "Uniform Resource Identifiers (URI): Generic Syntax and Semantics", T.
     Berners-Lee, R. Fielding, L. Masinter, 18 November 1997.
     Available at
     http://www.ics.uci.edu/pub/ietf/uri/draft-fielding-uri-syntax-01.txt.
     This is a work in progress that is expected to update [RFC1738] and
     [RFC1808].
[WEBSGML]
     "Proposed TC for WebSGML Adaptations for SGML", C. F. Goldfarb, ed., 14
     June 1997.
     Available at http://www.sgmlsource.com/8879rev/n1929.htm

Informative references

[BRYAN88]
     "SGML: An Author's Guide to the Standard Generalized Markup Language",
     M. Bryan, Addison-Wesley Publishing Co., 1988.
[CALS]
     Continuous Acquisition and Life-Cycle Support (CALS). CALS is a
     Department of Defense strategy for achieving effective creation,
     exchange, and use of digital data for weapon systems and equipment.
     More information can be found on the CALS home page at at
     http://navysgml.dt.navy.mil/cals.html.
[CHARSETS]
     Registered charset values. Download a list of registered charset values
     from ftp://ftp.isi.edu/in-notes/iana/assignments/character-sets.
[CSS2]
     "Cascading Style Sheets, level 2", B. Bos, H. W. Lie, C. Lilley, and I.
     Jacobs, November 1997.
     Available at http://www.w3.org/TR/WD-CSS2/
[DCORE]
     The Dublin Core: for more information see
     http://purl.org/metadata/dublin_core
[ETHNO]
     "Ethnologue, Languages of the World", 12th Edition, Barbara F. Grimes
     editor, Summer Institute of Linguistics, October 1992.
[GOLD90]
     "The SGML Handbook", C. F. Goldfarb, Clarendon Press, 1991.
[HTML30]
     "HyperText Markup Language Specification Version 3.0", Dave Raggett,
     September 1995.
     Available at http://www.w3.org/MarkUp/html3/CoverPage.
[HTML32]
     "HTML 3.2 Reference Specification", Dave Raggett, 14 January 1997.
     Available at http://www.w3.org/TR/REC-html32
[HTML3STYLE]
     "HTML and Style Sheets", B. Bos, D. Raggett, and H. Lie, 24 March 1997.
     Available at http://www.w3.org/TR/WD-style
[LEXHTML]
     "A Lexical Analyzer for HTML and Basic SGML", D. Connolly, 15 June
     1996. Available at http://www.w3.org/TR/WD-html-lex
[PICS]
     Platform for Internet Content (PICS). For more information see
     http://www.w3.org/PICS/
[RDF]
     The Resource Description Language: for more information see
     http://www.w3.org/Metadata/RDF/
[RFC822]
     "Standard for the Format of ARPA Internet Text Messages", Revised by
     David H. Crocker, August 1982.
     Available at http://ds.internic.net/rfc/rfc822.txt.
[RFC850]
     "Standard for Interchange of USENET Messages", M. Horton, June 1983.
     Available at http://ds.internic.net/rfc/rfc850.txt.
[RFC1468]
     "Japanese Character Encoding for Internet Messages", J. Murai, M.
     Crispin, and E. van der Poel, June 1993.
     Available at http://ds.internic.net/rfc/rfc1468.txt.
[RFC1630]
     "Universal Resource Identifiers in WWW: A Unifying Syntax for the
     Expression of Names and Addresses of Objects on the Network as used in
     the World-Wide Web", T. Berners-Lee, June 1994.
     Available at http://ds.internic.net/rfc/rfc1630.txt.
[RFC1866]
     "HyperText Markup Language 2.0", T. Berners-Lee and D. Connolly,
     November 1995.
     Available at http://ds.internic.net/rfc/rfc1866.txt.
[RFC1867]
     "Form-based File Upload in HTML", E. Nebel and L. Masinter, November
     1995.
     Available at http://ds.internic.net/rfc/rfc1867.txt. RFC1867 is
     expected to be updated by
     ftp://ftp.ietf.org/internet-drafts/draft-masinter-form-data-01.txt,
     currently a work in progress.
[RFC1942]
     "HTML Tables", Dave Raggett, May 1996.
     Available at http://ds.internic.net/rfc/rfc1942.txt.
[RFC2048]
     "Multipurpose Internet Mail Extensions (MIME) Part Four: Registration
     Procedures", N. Freed, J. Klensin, and J. Postel, November 1996.
     Available at http://ds.internic.net/rfc/rfc2048.txt. Note that this RFC
     obsoletes RFC1521, RFC1522, and RFC1590.
[RFC2070]
     "Internationalization of the HyperText Markup Language", F. Yergeau, G.
     Nicol, G. Adams, and M. Dürst, January 1997.
     Available at http://ds.internic.net/rfc/rfc2070.txt.
[SGMLOPEN]
     The SGML Consortium. Consult the home page of the SGML Consortium at
     http://www.sgmlopen.org/
[SP]
     SP is a public domain SGML parser.
     Available at ftp://ftp.jclark.com/pub/sp/. Further information is
     available at http://www.jclark.com.
[SQ91]
     "The SGML Primer", 3rd Edition, SoftQuad Inc., 1991.
[TAKADA]
     "Multilingual Information Exchange through the World-Wide Web",
     Toshihiro Takada, Computer Networks and ISDN Systems, Vol. 27, No. 2,
     pp. 235-241, November 1994.
[WAIGUIDE]
     Guidelines for designing accessible HTML documents are available at the
     Web Accessibility Initiative (WAI) Web site: http://www.w3.org/WAI/.
[VANH90]
     "Practical SGML", E. van Herwijnen, Kluwer Academic Publishers Group,
     Norwell and Dordrecht, 1990.

                             Index of Elements

  Legend: Optional, Forbidden, Empty, Deprecated, Loose DTD, Frameset DTD

    Name      Start   End  Empty Depr.DTD            Description
               Tag    Tag
 A                                                     anchor

 ABBR                                        abbreviated form (e.g., WWW,
                                                     HTTP, etc.)
 ACRONYM
 ADDRESS                                        information on author
 APPLET                            D   L             Java applet
 AREA                  F     E               client-side image map area
 B                                                 bold text style
 BASE                  F     E                    document base URI
 BASEFONT              F     E     D   L           base font size
 BDO                                             I18N BiDi over-ride
 BIG                                              large text style
 BLOCKQUOTE                                        long quotation
 BODY           O      O                            document body
 BR                    F     E                    forced line break
 BUTTON                                              push button
 CAPTION                                            table caption
 CENTER                            D   L   shorthand for DIV align=center
 CITE                                                 citation
 CODE                                          computer code fragment
 COL                   F     E                      table column
 COLGROUP              O                         table column group
 DD                    O                       definition description
 DEL                                                deleted text
 DFN                                             instance definition
 DIR                               D   L           directory list
 DIV                                      generic language/style container
 DL                                                definition list
 DT                    O                           definition term
 EM                                                   emphasis
 FIELDSET                                        form control group
 FONT                              D   L        local change to font
 FORM                                             interactive form
 FRAME                 F     E         F              subwindow
 FRAMESET                              F         window subdivision
 H1                                                    heading
 H2                                                    heading
 H3                                                    heading
 H4                                                    heading
 H5                                                    heading
 H6                                                    heading
 HEAD           O      O                            document head
 HR                    F     E                     horizontal rule
 HTML           O      O                        document root element
 I                                                italic text style
 IFRAME                                L          inline subwindow
 IMG                   F     E                     Embedded image
 INPUT                 F     E                      form control
 INS                                                inserted text
 ISINDEX               F     E     D   L         single line prompt
 KBD                                       text to be entered by the user
 LABEL                                          form field label text
 LEGEND                                            fieldset legend
 LI                    O                              list item
 LINK                  F     E                a media-independent link
 MAP                                            client-side image map
 MENU                              D   L              menu list
 META                  F     E                 generic metainformation

 NOFRAMES                              F   alternate content container for
                                              non frame-based rendering

 NOSCRIPT                                  alternate content container for
                                             non script-based rendering
 OBJECT                                        generic embedded object
 OL                                                 ordered list
 OPTGROUP                                           option group
 OPTION                O                          selectable choice
 P                     O                              paragraph
 PARAM                 F     E                  named property value
 PRE                                              preformatted text
 Q                                             short inline quotation
 S                                 D   L     sstrike-through text style

 SAMP                                      sample program output, scripts,
                                                        etc.
 SCRIPT                                           script statements
 SELECT                                            option selector
 SMALL                                            small text style
 SPAN                                     generic language/style container
 STRIKE                            D   L         strike-through text
 STRONG                                            strong emphasis
 STYLE                                               style info
 SUB                                                  subscript
 SUP                                                 superscript
 TABLE
 TBODY          O      O                             table body
 TD                    O                           table data cell
 TEXTAREA                                       multi-line text field
 TFOOT                 O                            table footer
 TH                    O                          table header cell
 THEAD                 O                            table header
 TITLE                                             document title
 TR                    O                              table row
 TT                                       teletype or monospaced text style
 U                                 D   L        underlined text style
 UL                                                unordered list

 VAR                                      instance of a variable or program
                                                      argument

                            Index of Attributes

                Legend: Deprecated, Loose DTD, Frameset DTD

      Name       Related        Type            Default       Depr.DTD       Comment
                 Elements

 abbr            TD, TH        %Text;          #IMPLIED                  abbreviation for
                                                                           header cell

 accept-charset   FORM       %Charsets;        #IMPLIED                  list of supported
                                                                             charsets

 accept           INPUT    %ContentTypes;      #IMPLIED                 list of MIME types
                                                                         for file upload
                 A, AREA,
                 BUTTON,
 accesskey        INPUT,    %Character;        #IMPLIED                  accessibility key
                  LABEL,                                                    character
                 LEGEND,
                TEXTAREA

 action           FORM         %URI;          #REQUIRED                  server-side form
                                                                             handler
 align           CAPTION      %CAlign;         #IMPLIED         D   L   relative to table
                 APPLET,
 align           IFRAME,      %IAlign;         #IMPLIED         D   L       vertical or
               IMG, INPUT,                                             horizontal alignment
                 OBJECT
 align           LEGEND       %LAlign;         #IMPLIED         D   L  relative to fieldset

 align            TABLE       %TAlign;         #IMPLIED         D   L     table position
                                                                        relative to window

 align             HR      (left | center      #IMPLIED         D   L
                              | right)
                 DIV, H1,  (left | center
 align         H2, H3, H4,    | right |        #IMPLIED         D   L       align, text
                H5, H6, P     justify)                                      alignment
                   COL,
                COLGROUP,  (left | center
 align          TBODY, TD,    | right |        #IMPLIED
                TFOOT, TH,    justify |
                THEAD, TR      char)

 alink            BODY        %Color;          #IMPLIED         D   L    color of selected
                                                                              links
 alt             APPLET        %Text;          #IMPLIED         D   L   short description
 alt            AREA, IMG      %Text;         #REQUIRED                 short description
 alt              INPUT        CDATA           #IMPLIED                 short description

 archive         OBJECT        %URI;           #IMPLIED                   space separated
                                                                           archive list

 archive         APPLET        CDATA           #IMPLIED         D   L     comma separated
                                                                           archive list

 axis            TD, TH        CDATA           #IMPLIED                   names groups of
                                                                         related headers

 background       BODY         %URI;           #IMPLIED         D   L    texture tile for
                                                                       document background

 bgcolor          TABLE       %Color;          #IMPLIED         D   L  background color for
                                                                              cells

 bgcolor           TR         %Color;          #IMPLIED         D   L  background color for
                                                                               row

 bgcolor         TD, TH       %Color;          #IMPLIED         D   L     cell background
                                                                              color

 bgcolor          BODY        %Color;          #IMPLIED         D   L   document background
                                                                              color
 border        IMG, OBJECT    %Length;         #IMPLIED         D   L   link border width

 border           TABLE       %Pixels;         #IMPLIED                controls frame width
                                                                           around table
 cellpadding      TABLE       %Length;         #IMPLIED                spacing within cells

 cellspacing      TABLE       %Length;         #IMPLIED                   spacing between
                                                                              cells
                   COL,
                COLGROUP,
 char           TBODY, TD,  %Character;        #IMPLIED                alignment char, e.g.
                TFOOT, TH,                                                   char=':'
                THEAD, TR
                   COL,
                COLGROUP,
 charoff        TBODY, TD,    %Length;         #IMPLIED                offset for alignment
                TFOOT, TH,                                                     char
                THEAD, TR

 charset         A, LINK,    %Charset;         #IMPLIED                  char encoding of
                 SCRIPT                                                  linked resource

 checked          INPUT      (checked)         #IMPLIED                  for radio buttons
                                                                         and check boxes

 cite          BLOCKQUOTE,     %URI;           #IMPLIED                   URI for source
                    Q                                                    document or msg

 cite           DEL, INS       %URI;           #IMPLIED                 info on reason for
                                                                              change
                   All
                 elements
                but BASE,
                BASEFONT,
 class         HEAD, HTML,     CDATA           #IMPLIED                space separated list
                  META,                                                     of classes
                  PARAM,
                 SCRIPT,
                  STYLE,
                  TITLE

 classid         OBJECT        %URI;           #IMPLIED                    identifies an
                                                                          implementation

 clear             BR       (left | all |        none           D   L  control of text flow
                           right | none)
 code            APPLET        CDATA           #IMPLIED         D   L   applet class file
                                                                           base URI for
 codebase        OBJECT        %URI;           #IMPLIED                   classid, data,
                                                                             archive

 codebase        APPLET        %URI;           #IMPLIED         D   L    optional base URI
                                                                            for applet

 codetype        OBJECT    %ContentType;       #IMPLIED                  content type for
                                                                               code

 color          BASEFONT,     %Color;          #IMPLIED         D   L       text color
                  FONT
                                                                         list of lengths,
 cols           FRAMESET   %MultiLengths;      #IMPLIED             F    default: 100% (1
                                                                               col)
 cols           TEXTAREA       NUMBER         #REQUIRED

 colspan         TD, TH        NUMBER             1                       number of cols
                                                                         spanned by cell
 compact        DIR, MENU    (compact)         #IMPLIED         D   L

 compact       DL, OL, UL    (compact)         #IMPLIED         D   L    reduced interitem
                                                                             spacing

 content          META         CDATA          #REQUIRED                     associated
                                                                           information

 coords           AREA        %Coords;         #IMPLIED                comma separated list
                                                                            of lengths
                                                                           for use with
 coords             A         %Coords;         #IMPLIED                  client-side image
                                                                               maps

 data            OBJECT        %URI;           #IMPLIED                    reference to
                                                                          object's data

 datetime       DEL, INS     %Datetime;        #IMPLIED                  date and time of
                                                                              change

 declare         OBJECT      (declare)         #IMPLIED                  declare but don't
                                                                         instantiate flag

 defer           SCRIPT       (defer)          #IMPLIED                    UA may defer
                                                                       execution of script
                   All
                 elements
               but APPLET,
                  BASE,
                BASEFONT,
 dir             BDO, BR,   (ltr | rtl)        #IMPLIED                    direction for
                  FRAME,                                                weak/neutral text
                FRAMESET,
               HR, IFRAME,
                  PARAM,
                 SCRIPT
 dir               BDO      (ltr | rtl)       #REQUIRED                   directionality
                 BUTTON,
                  INPUT,
 disabled       OPTGROUP,    (disabled)        #IMPLIED                 unavailable in this
                 OPTION,                                                     context
                 SELECT,
                TEXTAREA

 enctype          FORM     %ContentType;  "application/x-www-
                                           form-urlencoded"

 face           BASEFONT,      CDATA           #IMPLIED         D   L  comma separated list
                  FONT                                                    of font names

 for              LABEL        IDREF           #IMPLIED                  matches field ID
                                                                              value

 frame            TABLE       %TFrame;         #IMPLIED                which parts of frame
                                                                            to render

 frameborder      FRAME,      (1 | 0)             1                 F      request frame
                 IFRAME                                                      borders?

 headers         TD, TH        IDREFS          #IMPLIED                  list of id's for
                                                                           header cells
 height          IFRAME       %Length;         #IMPLIED             L      frame height
 height        IMG, OBJECT    %Length;         #IMPLIED                  override height
 height          APPLET       %Length;        #REQUIRED         D   L     initial height
 height          TD, TH       %Pixels;         #IMPLIED         D   L    height for cell

 href            A, AREA,      %URI;           #IMPLIED                   URI for linked
                  LINK                                                       resource

 href             BASE         %URI;           #IMPLIED         D   L    URI that acts as
                                                                             base URI
 hreflang        A, LINK   %LanguageCode;      #IMPLIED                   language code

 hspace          APPLET,      %Pixels;         #IMPLIED         D   L   horizontal gutter
               IMG, OBJECT

 http-equiv       META          NAME           #IMPLIED                HTTP response header
                                                                               name
                   All
                 elements
                but BASE,
 id            HEAD, HTML,       ID            #IMPLIED                document-wide unique
                  META,                                                         id
                 SCRIPT,
                  STYLE,
                  TITLE

 ismap             IMG        (ismap)          #IMPLIED                   use server-side
                                                                            image map

 label           OPTION        %Text;          #IMPLIED                     for use in
                                                                        hierarchical menus

 label          OPTGROUP       %Text;         #REQUIRED                     for use in
                                                                        hierarchical menus
                   All
                 elements
               but APPLET,
                  BASE,
 lang           BASEFONT,  %LanguageCode;      #IMPLIED                   language code
                BR, FRAME,
                FRAMESET,
               HR, IFRAME,
                  PARAM,
                 SCRIPT

 language        SCRIPT        CDATA           #IMPLIED                  predefined script
                                                                          language name
 link             BODY        %Color;          #IMPLIED         D   L     color of links
                                                                           link to long
 longdesc          IMG         %URI;           #IMPLIED                     description
                                                                        (complements alt)
                                                                           link to long
 longdesc         FRAME,       %URI;           #IMPLIED             F       description
                 IFRAME
                                                                       (complements title)

 marginheight     FRAME,      %Pixels;         #IMPLIED             F    margin height in
                 IFRAME                                                       pixels

 marginwidth      FRAME,      %Pixels;         #IMPLIED             F    margin widths in
                 IFRAME                                                       pixels

 maxlength        INPUT        NUMBER          #IMPLIED                 max chars for text
                                                                              fields

 media            STYLE     %MediaDesc;        #IMPLIED                  designed for use
                                                                         with these media

 media            LINK      %MediaDesc;        #IMPLIED                  for rendering on
                                                                           these media

 method           FORM      (GET | POST)         GET                    HTTP method used to
                                                                         submit the form

 multiple        SELECT      (multiple)        #IMPLIED                  default is single
                                                                            selection

 name            BUTTON,       CDATA           #IMPLIED
                TEXTAREA

 name            APPLET        CDATA           #IMPLIED         D   L    allows applets to
                                                                         find each other
 name            SELECT        CDATA           #IMPLIED                     field name

 name             FRAME,       CDATA           #IMPLIED             F    name of frame for
                 IFRAME                                                     targetting
 name               A          CDATA           #IMPLIED                   named link end

 name             INPUT,       CDATA           #IMPLIED                  submit as part of
                 OBJECT                                                        form

 name              MAP         CDATA          #REQUIRED                  for reference by
                                                                              usemap
 name             PARAM        CDATA          #REQUIRED                   property name
 name             META          NAME           #IMPLIED                metainformation name

 nohref           AREA        (nohref)         #IMPLIED                 this region has no
                                                                              action

 noresize         FRAME      (noresize)        #IMPLIED             F     allow users to
                                                                          resize frames?
 noshade           HR        (noshade)         #IMPLIED         D   L
 nowrap          TD, TH       (nowrap)         #IMPLIED         D   L   suppress word wrap

 object          APPLET        CDATA           #IMPLIED         D   L    serialized applet
                                                                               file
                 A, AREA,
                 BUTTON,
 onblur           INPUT,      %Script;         #IMPLIED                the element lost the
                  LABEL,                                                      focus
                 SELECT,
                TEXTAREA
                  INPUT,
 onchange        SELECT,      %Script;         #IMPLIED                  the element value
                TEXTAREA                                                   was changed
                   All
                 elements
               but APPLET,
                  BASE,
                BASEFONT,
                 BDO, BR,
                  FONT,
                  FRAME,
 onclick        FRAMESET,     %Script;         #IMPLIED                a pointer button was
               HEAD, HTML,                                                   clicked
                 IFRAME,
                 ISINDEX,
                  META,
                  PARAM,
                 SCRIPT,
                  STYLE,
                  TITLE
                   All
                 elements
               but APPLET,
                  BASE,
                BASEFONT,
                 BDO, BR,
                  FONT,
                  FRAME,
 ondblclick     FRAMESET,     %Script;         #IMPLIED                a pointer button was
               HEAD, HTML,                                                double clicked
                 IFRAME,
                 ISINDEX,
                  META,
                  PARAM,
                 SCRIPT,
                  STYLE,
                  TITLE
                 A, AREA,
                 BUTTON,
 onfocus          INPUT,      %Script;         #IMPLIED                 the element got the
                  LABEL,                                                      focus
                 SELECT,
                TEXTAREA
                   All
                 elements
               but APPLET,
                  BASE,
                BASEFONT,
                 BDO, BR,
                  FONT,
                  FRAME,
 onkeydown      FRAMESET,     %Script;         #IMPLIED                  a key was pressed
               HEAD, HTML,                                                     down
                 IFRAME,
                 ISINDEX,
                  META,
                  PARAM,
                 SCRIPT,
                  STYLE,
                  TITLE
                   All
                 elements
               but APPLET,
                  BASE,
                BASEFONT,
                 BDO, BR,
                  FONT,
                  FRAME,
 onkeypress     FRAMESET,     %Script;         #IMPLIED                  a key was pressed
               HEAD, HTML,                                                 and released
                 IFRAME,
                 ISINDEX,
                  META,
                  PARAM,
                 SCRIPT,
                  STYLE,
                  TITLE
                   All
                 elements
               but APPLET,
                  BASE,
                BASEFONT,
                 BDO, BR,
                  FONT,
                  FRAME,
 onkeyup        FRAMESET,     %Script;         #IMPLIED                 a key was released
               HEAD, HTML,
                 IFRAME,
                 ISINDEX,
                  META,
                  PARAM,
                 SCRIPT,
                  STYLE,
                  TITLE

 onload         FRAMESET      %Script;         #IMPLIED             F   all the frames have
                                                                           been loaded

 onload           BODY        %Script;         #IMPLIED                  the document has
                                                                           been loaded
                   All
                 elements
               but APPLET,
                  BASE,
                BASEFONT,
                 BDO, BR,
                  FONT,
                  FRAME,
 onmousedown    FRAMESET,     %Script;         #IMPLIED                a pointer button was
               HEAD, HTML,                                                 pressed down
                 IFRAME,
                 ISINDEX,
                  META,
                  PARAM,
                 SCRIPT,
                  STYLE,
                  TITLE
                   All
                 elements
               but APPLET,
                  BASE,
                BASEFONT,
                 BDO, BR,
                  FONT,
                  FRAME,
 onmousemove    FRAMESET,     %Script;         #IMPLIED                 a pointer was moved
               HEAD, HTML,                                                    within
                 IFRAME,
                 ISINDEX,
                  META,
                  PARAM,
                 SCRIPT,
                  STYLE,
                  TITLE
                   All
                 elements
               but APPLET,
                  BASE,
                BASEFONT,
                 BDO, BR,
                  FONT,
                  FRAME,
 onmouseout     FRAMESET,     %Script;         #IMPLIED                 a pointer was moved
               HEAD, HTML,                                                     away
                 IFRAME,
                 ISINDEX,
                  META,
                  PARAM,
                 SCRIPT,
                  STYLE,
                  TITLE
                   All
                 elements
               but APPLET,
                  BASE,
                BASEFONT,
                 BDO, BR,
                  FONT,
                  FRAME,
 onmouseover    FRAMESET,     %Script;         #IMPLIED                 a pointer was moved
               HEAD, HTML,                                                     onto
                 IFRAME,
                 ISINDEX,
                  META,
                  PARAM,
                 SCRIPT,
                  STYLE,
                  TITLE
                   All
                 elements
               but APPLET,
                  BASE,
                BASEFONT,
                 BDO, BR,
                  FONT,
                  FRAME,
 onmouseup      FRAMESET,     %Script;         #IMPLIED                a pointer button was
               HEAD, HTML,                                                   released
                 IFRAME,
                 ISINDEX,
                  META,
                  PARAM,
                 SCRIPT,
                  STYLE,
                  TITLE
 onreset          FORM        %Script;         #IMPLIED                 the form was reset

 onselect         INPUT,      %Script;         #IMPLIED                    some text was
                TEXTAREA                                                     selected

 onsubmit         FORM        %Script;         #IMPLIED                    the form was
                                                                            submitted

 onunload       FRAMESET      %Script;         #IMPLIED             F   all the frames have
                                                                           been removed

 onunload         BODY        %Script;         #IMPLIED                  the document has
                                                                           been removed

 profile          HEAD         %URI;           #IMPLIED                 named dictionary of
                                                                            meta info
 prompt          ISINDEX       %Text;          #IMPLIED         D   L     prompt message
 readonly       TEXTAREA     (readonly)        #IMPLIED
 readonly         INPUT      (readonly)        #IMPLIED                for text and passwd
 rel             A, LINK    %LinkTypes;        #IMPLIED                 forward link types
 rev             A, LINK    %LinkTypes;        #IMPLIED                 reverse link types
                                                                         list of lengths,
 rows           FRAMESET   %MultiLengths;      #IMPLIED             F    default: 100% (1
                                                                               row)
 rows           TEXTAREA       NUMBER         #REQUIRED

 rowspan         TD, TH        NUMBER             1                       number of rows
                                                                         spanned by cell

 rules            TABLE       %TRules;         #IMPLIED                rulings between rows
                                                                             and cols

 scheme           META         CDATA           #IMPLIED                   select form of
                                                                             content

 scope           TD, TH       %Scope;          #IMPLIED                  scope covered by
                                                                           header cells

 scrolling        FRAME,     (yes | no |         auto               F   scrollbar or none
                 IFRAME        auto)
 selected        OPTION      (selected)        #IMPLIED
                                                                             controls
 shape            AREA        %Shape;            rect                    interpretation of
                                                                              coords
                                                                           for use with
 shape              A         %Shape;            rect                    client-side image
                                                                               maps
 size              HR         %Pixels;         #IMPLIED         D   L

 size             FONT         CDATA           #IMPLIED         D   L      [+|-]nn e.g.
                                                                       size="+1", size="4"

 size             INPUT        CDATA           #IMPLIED                  specific to each
                                                                          type of field

 size           BASEFONT       CDATA          #REQUIRED         D   L   base font size for
                                                                          FONT elements
 size            SELECT        NUMBER          #IMPLIED                    rows visible

 span              COL         NUMBER             1                       COL attributes
                                                                         affect N columns

 span           COLGROUP       NUMBER             1                      default number of
                                                                         columns in group

 src             SCRIPT        %URI;           #IMPLIED                 URI for an external
                                                                              script

 src              INPUT        %URI;           #IMPLIED                   for fields with
                                                                              images

 src              FRAME,       %URI;           #IMPLIED             F     source of frame
                 IFRAME                                                      content

 src               IMG         %URI;          #REQUIRED                   URI of image to
                                                                              embed

 standby         OBJECT        %Text;          #IMPLIED                   message to show
                                                                          while loading

 start             OL          NUMBER          #IMPLIED         D   L    starting sequence
                                                                              number
                   All
                 elements
                but BASE,
                BASEFONT,
 style         HEAD, HTML,  %StyleSheet;       #IMPLIED                  associated style
                  META,                                                        info
                  PARAM,
                 SCRIPT,
                  STYLE,
                  TITLE

 summary          TABLE        %Text;          #IMPLIED                  purpose/structure
                                                                        for speech output
                 A, AREA,
                 BUTTON,
 tabindex         INPUT,       NUMBER          #IMPLIED                 position in tabbing
                 OBJECT,                                                      order
                 SELECT,
                TEXTAREA
                 A, AREA,
 target        BASE, FORM, %FrameTarget;       #IMPLIED         D   L  render in this frame
                  LINK
 text             BODY        %Color;          #IMPLIED         D   L  document text color
 title            STYLE        %Text;          #IMPLIED                   advisory title
                   All
                 elements
                but BASE,
                BASEFONT,
 title         HEAD, HTML,     %Text;          #IMPLIED                      advisory
                  META,                                                title/amplification
                  PARAM,
                 SCRIPT,
                  STYLE,
                  TITLE

 type            A, LINK   %ContentType;       #IMPLIED                  advisory content
                                                                               type

 type            OBJECT    %ContentType;       #IMPLIED                  content type for
                                                                               data
                                                                         content type for
 type             PARAM    %ContentType;       #IMPLIED                     value when
                                                                          valuetype=ref

 type            SCRIPT    %ContentType;      #REQUIRED                   content type of
                                                                         script language

 type             STYLE    %ContentType;      #REQUIRED                   content type of
                                                                          style language

 type             INPUT     %InputType;          TEXT                   what kind of widget
                                                                            is needed
 type              LI        %LIStyle;         #IMPLIED         D   L    list item style
 type              OL        %OLStyle;         #IMPLIED         D   L    numbering style
 type              UL        %ULStyle;         #IMPLIED         D   L      bullet style
                              (button |
 type            BUTTON       submit |          submit                    for use as form
                               reset)                                         button

 usemap        IMG, INPUT,     %URI;           #IMPLIED                   use client-side
                 OBJECT                                                     image map
                   COL,
                COLGROUP,   (top | middle
 valign         TBODY, TD,   | bottom |        #IMPLIED                 vertical alignment
                TFOOT, TH,   baseline)                                       in cells
                THEAD, TR

 value           OPTION        CDATA           #IMPLIED                 defaults to element
                                                                             content
 value            PARAM        CDATA           #IMPLIED                   property value

 value            INPUT        CDATA           #IMPLIED                 required for radio
                                                                          and checkboxes

 value           BUTTON        CDATA           #IMPLIED                 sent to server when
                                                                            submitted

 value             LI          NUMBER          #IMPLIED         D   L     reset sequence
                                                                              number

 valuetype        PARAM     (DATA | REF |        DATA                    How to interpret
                              OBJECT)                                         value
 version          HTML         CDATA        %HTML.Version;      D   L        Constant

 vlink            BODY        %Color;          #IMPLIED         D   L    color of visited
                                                                              links

 vspace          APPLET,      %Pixels;         #IMPLIED         D   L    vertical gutter
               IMG, OBJECT
 width             HR         %Length;         #IMPLIED         D   L
 width           IFRAME       %Length;         #IMPLIED             L      frame width
 width         IMG, OBJECT    %Length;         #IMPLIED                   override width
 width            TABLE       %Length;         #IMPLIED                    table width
 width           APPLET       %Length;        #REQUIRED         D   L     initial width

 width             COL     %MultiLength;       #IMPLIED                    column width
                                                                          specification

 width          COLGROUP   %MultiLength;       #IMPLIED                  default width for
                                                                          enclosed COLs
 width           TD, TH       %Pixels;         #IMPLIED         D   L     width for cell
 width             PRE         NUMBER          #IMPLIED         D   L

