lilypond conditionals?

[Karl Berry]

Does lilypond have some form of conditionals (at the source level)?

In my case, I have a piece which I'd like to separately print the top
line + tablature, the bottom line + tablature, and the top line + bottom
line (and change the headings accordingly).

I've just been commenting out the appropriate blocks to make this
happen, but it would be nicer if I could do it with one setting.

Thanks,
karl