Determine and output counter values at line breaks

[Urs Liska]

Hi all,

I am thinking about the option to produce an intermediate output file 
during a LilyPond compilation. This should contain information on a 
number of counter values at all line breaks. Currently I see barnumbers 
(optionally measure position when the break is in mid-measure) and mark 
numbers, but there might be more.

The idea is that I'd like to try creating a set-up where I can ask 
LilyPond to only compile a given range of the score. For this I'd need 
to determine the points to set skipTypesetting commands and the data to 
set the counters. If combined with the system-wise output using 
lilypond-book-preamble or something derived from that I'm thinking if 
it's possible to create a music view interface that doesn't display 
pages but a series of systems, and where upon editing (usually) only one 
system has to be recompiled and the system replaced.

So, what I'd need for this is a hint where to start hooking into the 
compilation process to determine these counter values upon each line break.

I still don't have any clue about these things and still wait for 
someone writing a few nice tutorials on the blog, but I have the idea 
that engravers and listeners is where I should start looking.

TIA
Urs