Doc: document grob metadata in SVG output in Notation Reference (issue 357720044 by address@hidden)

[paulwmorris]

Reviewers: ,

Message:
Please review, thanks, -Paul

Description:
Doc: document grob metadata in SVG output in Notation Reference

I.e. using the 'output-attributes' grob property to add id, class,
and other attributes to the SVG output for a given grob.

Please review this at https://codereview.appspot.com/357720044/

Affected files (+35, -1 lines):
  M Documentation/notation/input.itely


Index: Documentation/notation/input.itely
diff --git a/Documentation/notation/input.itely  
b/Documentation/notation/input.itely
index  
f31d23086fda0aa31dbe72b32cbfe88a5f302a63..247cb0dba592228aec0ff5d99e3946cce122a2d8  
100644
--- a/Documentation/notation/input.itely
+++ b/Documentation/notation/input.itely
@@ -2774,9 +2774,43 @@ voices and staves, saving even more time.
 The default output formats for the printed score are Portable
 Document Format (PDF) and PostScript (PS).  Portable
 Network Graphics (PNG), Scalable Vector Graphics (SVG) and Encapsulated
-PostScript (EPS) output is available through the command line option,
+PostScript (EPS) output is available through command line options,
 see @rprogram{Basic command line options for LilyPond}.

address@hidden SVG Output
address@hidden SVG Output
+
+SVG output can optionally contain metadata for graphical objects (grobs)  
like
+note heads, rests, etc.  This metadata can be standard SVG attributes like
address@hidden and @code{class}, or non-standard custom attributes.  Specify the
+attributes and their values by overriding a grob's @code{output-attributes}
+property with a Scheme association list (alist).  The values can be  
numbers,
+strings, or symbols.  For example:
+
address@hidden
address@hidden
+  \once \override NoteHead.output-attributes =
+  #'((id . 123)
+     (class . "this that")
+     (data-whatever . something))
+  c
address@hidden
address@hidden example
+
address@hidden
+The input above will produce the following @code{<g>} (group) tag in the  
SVG
+file:
+
address@hidden
+<g id="123" class="this that" data-whatever="something">
+  ...NoteHead grob SVG elements...
+</g>
address@hidden example
+
address@hidden
+The @code{<g>} tag contains all of the SVG elements for a given grob.   
(Some
+grobs generate multiple SVG elements.)  In SVG syntax the @code{data-}  
prefix
+is used for non-standard custom metadata attributes.

 @node Replacing the notation font
 @subsection Replacing the notation font