limitations of define-markup-command -- undocumented yet

[Werner LEMBERG]

As a follow-up to my answer of Hai-Peng's problem I wonder whether the
parser limitations of define-markup-command are documented somewhere,
this is, which exact combination of arguments are supported (in the
docs of 2.11.42 this is missing).

Looking into parser.yy, I see these combinations:

  %token <scm> MARKUP_HEAD_EMPTY
  %token <scm> MARKUP_HEAD_LIST0
  %token <scm> MARKUP_HEAD_MARKUP0
  %token <scm> MARKUP_HEAD_MARKUP0_MARKUP1
  %token <scm> MARKUP_HEAD_SCM0
  %token <scm> MARKUP_HEAD_SCM0_MARKUP1
  %token <scm> MARKUP_HEAD_SCM0_SCM1
  %token <scm> MARKUP_HEAD_SCM0_SCM1_MARKUP2
  %token <scm> MARKUP_HEAD_SCM0_MARKUP1_MARKUP2
  %token <scm> MARKUP_HEAD_SCM0_SCM1_SCM2

[So there's indeed no MARKUP_HEAD_SCM0_SCM1_SCM2_SCM3 as Hai-Peng
 would have needed.]

It's a non-trivial issue for Joe User to find that, and the error
message is really cryptic if you don't know what a `signature' within
Scheme means.


    Werner