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/*!
    \page plugin-specifications.html
    \title Plugin Specifications

    The specification of a plugin is an XML file that contains all
    information that is necessary for loading the plugin's library,
    determining whether plugins are to be loaded and in which order (depending
    on e.g. dependencies). In addition, it contains textual descriptions of
    who created the plugin, what it is for, and where to find more information about it.
    The file must be located in (a subdir of) one of the plugin manager's
    plugin search paths, and must have the \c .pluginspec extension.

    \section2 Main Tag

    The root tag is \c plugin. It has the mandatory attributes \c name
    and \c version, and the optional attributes \c compatVersion, \c experimental
    and \c disabledByDefault.
    \table
        \header
            \o Tag
            \o Meaning
        \row
            \o plugin
            \o Root element in a plugin's XML file.
    \endtable
    \table
        \header
            \o Attribute
            \o Meaning
        \row
            \o name
            \o This is used as an identifier for the plugin and can e.g.
               be referenced in other plugin's dependencies. It is
               also used to construct the name of the plugin library
               as \c{lib[name].[dll|.so|.dylib]}. (Depending on platform.
               If you use the same string as the \c TARGET in your plugin's
               .pro-file, you are fine.)
        \row
            \o version
            \o Version string in the form \c{x.y.z_n}, used for identifying
               the plugin. Also see \l{A Note on Plugin Versions}.
        \row
            \o compatVersion
            \o Optional. If not given, it is implicitly
               set to the same value as \c version. The compatibility version
               states which version of this plugin the current version is
               binary backward compatible with and is used to resolve dependencies
               on this plugin. I.e. a \c version of \c{2.1.1} and a
               \c compatVersion of \c{2.0.0} means that this version \c{2.1.1} of the plugin
               is binary backward compatible with all versions of the plugin down to \c{2.0.0}
               (inclusive).
        \row
            \o experimental
            \o Optional. Can be \c true or \c false, defaults to \c false.
               Experimental plugins are not loaded by default but must be explicitly
               enabled by the user. This attribute should be enabled for new plugins which have the
               potential to negatively affect the user experience.
        \row
            \o disabledByDefault
            \o Optional. Can be \c true or \c false, defaults to \c false.
               If set, the respective plugin is not loaded by default but must be explicitly
               enabled by the user. This should be done for plugins which are not expected
               to be used by so many people as to justify the additional resource consumption.
    \endtable

    \section2 Plugin-describing Tags

    These are direct children of the \c plugin tag, and are solely used
    for more detailed (user centric) description of the plugin. All of these
    are optional.
    \table
        \header
            \o Tag
            \o Meaning
        \row
            \o category
            \o Defaults to \c Utilities. Is used to put related plugins
               under the same tree node in the plugin overview \gui{About Plugins...}.
        \row
            \o vendor
            \o String that describes the plugin creator/vendor,
               like \c{MyCompany}.
        \row
            \o copyright
            \o A short copyright notice, like \c{(C) 2007-2008 MyCompany}.
        \row
            \o license
            \o Possibly multi-line license information about the plugin.
               Should still be kept relatively short, since the UI is not
           designed for long texts.
        \row
            \o description
            \o Possibly multi-line description of what the plugin is supposed
               to provide.
               Should still be kept relatively short, since the UI is not
           designed for long texts.
        \row
            \o url
            \o Link to further information about the plugin, like
               \c{http://www.mycompany-online.com/products/greatplugin}.
    \endtable

    \section2 Dependencies

    A plugin can have dependencies on other plugins. These are
    specified in the plugin description, to ensure that
    these other plugins are loaded before this plugin.

    The XML element that describes a single dependency is the \c dependency tag,
    with required attributes \c name and \c version. All \c dependency tags
    must be enclosed in a single \c dependencyList tag, which is an optional
    child of the \c plugin tag.

    The following formulas illustrate how the dependency information is matched.
    In the formulas the name of the required plugin (as defined in the attributes
    of the \c dependency tag) is denoted as \c dependencyName
    and the required version of the plugin is denoted as \c dependencyVersion.
    A plugin with given \c name, \c version and \c compatVersion
    (as defined in the attributes of the plugin's \c plugin tag) matches
    the dependency if
    \list
        \o its \c name matches \c dependencyName, and
        \o \c {compatVersion <= dependencyVersion <= version}.
    \endlist
    For example a dependency
    \code
        <dependency name="SomeOtherPlugin" version="2.3.0_2"/>
    \endcode
    would be matched by a plugin with
    \code
        <plugin name="SomeOtherPlugin" version="3.1.0" compatVersion="2.2.0">
    \endcode
    since the name matches, and the version \c{2.3.0_2} given in the dependency tag
    lies in the range of \c{2.2.0} and \c{3.1.0}.

    \table
        \header
            \o Tag
            \o Meaning
        \row
            \o dependency
            \o Describes a dependency on another plugin.
    \endtable
    \table
        \header
            \o Attribute
            \o Meaning
        \row
            \o name
            \o The name of the plugin, on which this plugin relies.
        \row
            \o version
            \o The version to which the plugin must be compatible to
               fill the dependency, in the form \c{x.y.z_n}.
               Can be empty if the version does not matter.
        \row
            \o type
        \o Optional. Value \c required or \c optional. Defines if the dependency is
           a hard requirement or optional. Defaults to \c{required}.
    \endtable

    \section3 Optional Dependencies

    A plugin can specify that a dependency on another plugin is optional, by adding the
    \c {type="optional"} attribute to the \c dependency tag:

    \list
        \o If the dependency can be resolved, the plugin and
           its dependency are loaded and initialized as for \c required dependencies.
        \o If the dependency cannot be resolved, the plugin is loaded and initialized
           as if the dependency was not declared at all.
    \endlist

    The plugin is not informed about the existence of optional dependencies in any way. Since the
    dependency might be loaded or not, the plugin may also not link against the dependency.
    A common way to access objects from optional dependencies is to get the object from the
    \l{The Plugin Manager, the Object Pool, and Registered Objects}{global object pool}
    via ExtensionSystem::PluginManager::getObjectByName() or
    ExtensionSystem::PluginManager::getObjectByClassName(), and use QMetaObject functions to call
    methods on it.

    \section2 Command Line Arguments

    Plugins can register command line arguments that the user can give
    when starting the application. These command line arguments are shown
    with a one-line description when the user runs the application with
    the \c{-help} command line argument, and the plugin manager does its command
    line parsing and sanity checks based on that information.
    If the plugin manager finds matching command line arguments for a plugin,
    it passes them on to the plugin's
    \l{ExtensionSystem::IPlugin::initialize()}{initialize()} method.

    All command line argument definitions are enclosed by a single \c argumentList
    tag. The individual command line arguments are defined by the \c argument tag,
    with required attribute \c name and an optional attribute \c parameter if the
    command line argument takes an additional parameter. The text that is enclosed
    in the \c argument tag is used as a (one-line) description in the command line
    argument help.

    \table
        \header
            \o Tag
            \o Meaning
        \row
            \o argument
            \o Describes a command line argument that the plugin wants to handle.
    \endtable
    \table
        \header
            \o Attribute
            \o Meaning
        \row
            \o name
            \o The command line argument itself, including the \c - prefix, e.g.
               \c{-my-parameter}.
        \row
            \o parameter
            \o Optional. If this is given, the command line argument expects an
               additional parameter, e.g. \c{-my-parameter somevalue}. The
               value of this attribute is used as a very short description of the
               parameter for the user.
    \endtable

    \section2 Example \c Test.pluginspec

    \code
    <plugin name="Test" version="1.0.1" compatVersion="1.0.0">
            <vendor>MyCompany</vendor>
            <copyright>(C) 2007 MyCompany</copyright>
            <license>
        This is a default license bla
        blubbblubb
        end of terms
            </license>
            <description>
        This plugin is just a test.
        it demonstrates the great use of the plugin spec.
            </description>
            <url>http://www.mycompany-online.com/products/greatplugin</url>
            <dependencyList>
                <dependency name="SomeOtherPlugin" version="2.3.0_2"/>
                <dependency name="EvenOther" version="1.0.0"/>
            </dependencyList>
            <argumentList>
                <argument name="-variant" parameter="fancy|boring">Brings up the fancy or boring user interface</argument>
            </argumentList>
        </plugin>
    \endcode

    \section2 A Note on Plugin Versions

    Plugin versions are in the form \c{x.y.z_n} where, \c x, \c y, \c z and \c n are
    non-negative integer numbers. You don't have to specify the version
    in this full form - any left-out part will implicitly be set to zero.
    So, \c{2.10_2} is equal to \c{2.10.0_2}, and \c 1 is the same as \c{1.0.0_0}.

*/
