Merge tag 'upstream/2.19.80' into debian-experimental

[lilypond.git] / Documentation / extending / programming-interface.itely

diff --git a/Documentation/extending/programming-interface.itely b/Documentation/extending/programming-interface.itely
index 5e63eabcd4f96598e64c742beca832dadfedf3ca..05da85a631cb913ea88e41a0213055307e9da784 100644 (file)
--- a/Documentation/extending/programming-interface.itely
+++ b/Documentation/extending/programming-interface.itely
@@ -1374,6 +1374,18 @@ can by found in the Internals Reference or the file 'define-grobs.scm':
 @}
 @end example
 
+It is also possible to get the value of the existing default by
+employing the function @code{grob-transformer}:
+
+@lilypond[verbatim,quote]
+\relative {
+  \override Flag.X-offset = #(grob-transformer 'X-offset
+    (lambda (flag default) (* default 4.0)))
+  c''4. d8 a4. g8
+}
+@end lilypond
+
+
 From within a callback, the easiest method for evaluating a markup is
 to use grob-interpret-markup.  For example: