+
+@item
+Each grob property can be a procedure. If this is the case, it is
+assumed to be a routine that calculates said property. This is a
+major internal cleanup, which also provides advanced tweakability for
+power users. For example,
+
+@verbatim
+\override Beam #'direction
+ = #(lambda (grob)
+ (if (> 4 (ly:grob-array-length (ly:grob-object grob 'stems)))
+ DOWN
+ UP))
+@end verbatim
+
+@noindent
+With this code fragment, the direction of a beam is decided to be up
+or down, depending on the number of stems in the beam.
+