LilyPond Notation Reference: 5.2.2 Layout interfaces

### 5.2.2 Layout interfaces

The HTML page that we found in the previous section describes the layout object called Fingering. Such an object is a symbol within the score. It has properties that store numbers (like thicknesses and directions), but also pointers to related objects. A layout object is also called a Grob, which is short for Graphical Object. For more details about Grobs, see grob-interface.

The page for `Fingering` lists the definitions for the `Fingering` object. For example, the page says

> `padding` (dimension, in staff space):

> `0.5`

which means that the number will be kept at a distance of at least 0.5 of the note head.

Each layout object may have several functions as a notational or typographical element. For example, the Fingering object has the following aspects

- Its size is independent of the horizontal spacing, unlike slurs or beams.
- It is a piece of text. Granted, it is usually a very short text.
- That piece of text is typeset with a font, unlike slurs or beams.
- Horizontally, the center of the symbol should be aligned to the center of the note head.
- Vertically, the symbol is placed next to the note and the staff.
- The vertical position is also coordinated with other superscript and subscript symbols.

Each of these aspects is captured in so-called interfaces, which are listed on the Fingering page at the bottom

> This object supports the following interfaces: item-interface, self-alignment-interface, side-position-interface, text-interface, text-script-interface, font-interface, finger-interface, and grob-interface.

Clicking any of the links will take you to the page of the respective object interface. Each interface has a number of properties. Some of them are not user-serviceable (‘Internal properties’), but others can be modified.

We have been talking of the `Fingering` object, but actually it does not amount to much. The initialization file (see Other sources of information) ‘`scm/define-grobs.scm`’ shows the soul of the ‘object’,

>     (Fingering
>       . ((padding . 0.5)
>          (avoid-slur . around)
>          (slur-padding . 0.2)
>          (staff-padding . 0.5)
>          (self-alignment-X . 0)
>          (self-alignment-Y . 0)
>          (script-priority . 100)
>          (stencil . ,ly:text-interface::print)
>          (direction . ,ly:script-interface::calc-direction)
>          (font-encoding . fetaText)
>          (font-size . -5) 		; don't overlap when next to heads.
>          (meta . ((class . Item)
>          (interfaces . (finger-interface
>                         font-interface
>                         text-script-interface
>                         text-interface
>                         side-position-interface
>                         self-alignment-interface
>                         item-interface))))))

As you can see, the `Fingering` object is nothing more than a bunch of variable settings, and the webpage in the Internals Reference is directly generated from this definition.

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