The Extending LilyPond manual, in section 1.3.4:
http://www.lilypond.org/doc/v2.19/Documentation/extending/adding-articulation-to-notes-_0028example_0029
currently states:
"Now we transform the add-accent function into a music function (a
matter of some syntactic sugar and a declaration of the type of its
sole ‘real’ argument).
addAccent = #(define-music-function (note-event)
(ly:music?)"
Now, the two words, "sole ‘real’" are mysterious and confusing, since
"note-event" is the only argument.
Formerly, those words referred to the fact that (in version 2.18) the
supplied arguments "parser" and "location" conveyed no information.
Compare version 2.18:
"Now we transform the add-accent function into a music function (a
matter of some syntactic sugar and a declaration of the type of its
sole ‘real’ argument).
addAccent = #(define-music-function (parser location note-event)
(ly:music?)"
So the present text should be changed to:
"Now we transform the add-accent function into a music function (a
matter of some syntactic sugar and a declaration of the type of its
argument).
addAccent = #(define-music-function (note-event)
(ly:music?)"