Extracting header fields for use by e.g. LaTeX?

[Michael Haynie]

Greetings;

I'm looking for a way to produce Table of Contents entries, Index 
entries, and song numbers for songs in a song book.  In Lilypond 2.2, I 
replaced the the LaTeX titling definitions to suit my needs, but that 
doesn't seem to be an option with 2.6.  Short of hacking scheme in some 
nonstandard way, it's not obvious to me how to proceed.  I'd like to 
avoid non-standard approaches, since they're likely to break with the 
next version of Lilypond.

Ideally, I'd like to have lilypond not set the titles directly -- just 
write a LaTeX snippet defining the relevant portions.  That way I can 
rely on LaTeX's excellent features.  TOC entries and index entries are 
relatively simple to manage.  The most difficult issue will be keeping 
track of song numbers and setting the song number on the right or left 
depending on whether the song is on a right hand page or left hand 
page.  That's easy to handle if the decision is made by LaTeX.  I think 
it would be impractical to have lilypond attempt that task.

Is that possible to accomplish with the current header handling 
mechanisms and lilypond-book?  What would the rough outline look like?

Thanks.