Multiple markings

[David Sumbler]

A text mark in Lilypond is represented by a grob called a
RehearsalMark; the grob for a tempo marking is called a MetronomeMark.

I wonder whether perhaps these names reflect something about the
history of Lilypond: they are certainly not accurate descriptions of
what the objects are used for - e.g. very often tempo markings make no
reference to a metronome.  I also suspect that history gives a clue to
why Lilypond allows only one of each of these objects at any point in a
score unless one performs some sort of programming acrobatics to work
around the restriction.

In fact this restriction, certainly in the case of RehearsalMark, has
no logic to it.  So either it is somehow hard-wired at a deep level, or
it must be there presumably because at one time it did make sense.

The clue is in the names, perhaps.  It generally does not make sense to
have more than one actual rehearsal mark at a single point in a piece
of music (although I can think of rare circumstances in which there
might be editorial reasons for doing so).  But the RehearsalMark object
is now not used only for rehearsal marks.  For instance, even according
to the documentation it is used for putting a fermata sign over a
barline.  Now, there is no reason on earth why a fermata sign and a
rehearsal mark should never appear at the same point, yet Lilypond
throws out a warning and refuses to print one of the objects unless we
go to extra lengths to get what we actually want.

A RehearsalMark is actually a very useful thing for aligning something
with a barline - just recently I wanted it for the titles of the
various sections of a piece.  Similarly, there might be times when the
alignment (or other) characteristics of MetronomeMark are useful for
some other text, which might or might not occur at the same point as an
actual tempo marking.

The only case where having more than one of either of these objects
causes a problem (only for midi output and easy for Lilypond to deal
with, even then) is if 2 actual metronome marks occur at the same
point.

Would it not make better sense for Lilypond to accept what is asked for
without complaining and print all the requested items?  We don't
actually need to have a warning about the supposed error if we can see 
the result in the output.  If it is a genuine mistake (e.g. putting
"Allegro" in most parts and "allegro" in another) then we can see that,
and it won't take long to locate the error.

So my question is: is there any good reason why Lilypond still does not
allow multiple marks or tempo markings?

If the answer to that question really is "yes", then perhaps we could
have an additional grob or 2 which have the same characteristics as the
existing one(s) but without the restriction on numbers.  E.g. could we
have a TextMark grob in addition to RehearsalMark?

David