Re: learning (names of) markup commands in scheme: documentation

[Lukas-Fabian Moser]

> Also note that your function, if called with \strut-line { hello world 
> }, actually adds your invisible strut to every word of the line. (Just 
> remove the make-transparent-markup in your function to see this, or, 
> more easuily, remove the #:transparent in my version). Compare:
>
> \markup \strut-line { hello world }
> \markup \strut-line \line { hello world }
>
> This difference (I think) originates in the way LilyPond applies 
> markup functions to explicit markups of the form { some word and some 
> other }, or put differently: Where the implicit \line is put, and how 
> a function expecting a single markup is applied to a list of markups.
>
> But note what changes if you replace the markup? predicate in your 
> function definition by markup-list?.

I think that was a bit cryptic :-).

Here's a (hopefully) clearer example:

\version "2.22"

#(define-markup-command (demo-eating-markup layout props stuff) (markup?)
   (format #t "Processing single markup: \"~a\"\n" (markup->string stuff))
   (interpret-markup layout props stuff))

#(define-markup-command (demo-eating-markup-list layout props stuff) 
(markup-list?)
   (format #t "Processing markup list: ~a\n" stuff)
   (interpret-markup layout props (make-column-markup stuff)))

\markup \demo-eating-markup { one two }
\markup \demo-eating-markup \line { eins zwei }
\markup \demo-eating-markup-list { oans zwoa }
\markup \demo-eating-markup-list { \line { un deux } }

The standard use case for make-XXX-markup is explained in: 
http://lilypond.org/doc/v2.23/Documentation/extending/markup-construction-in-scheme.html 
under "Known issues and warnings".

I would agree that the explanations regarding markups vs. markup lists, 
markup vs. stencils, markup in scheme etc. in the Documentation might be 
improved. We always welcome contributions! (And, your probably noticed 
this: The German documentation is in an effectively unmaintained state 
at the moment. But it seems there's hope this might change soonish.

Lukas