This rewrite was sponsored by Trent Johnston and John Mandereau.
@item
-Major internal cleanups: for each grob, a subproperty in
-@code{callbacks} property defines the procedure which computes it.
+For each grob, a subproperty in @code{callbacks} property defines the
+procedure which computes it. This is major internal cleanup, which
+also provides advanced tweakability for power users. For example,
@verbatim
\override Beam #'callbacks #'direction
= #(lambda (grob)
- (if (4 > (ly:grob-array-length (ly:grob-object 'stems)))
+ (if (> 4 (ly:grob-array-length (ly:grob-object grob 'stems)))
DOWN
UP))
@end verbatim