LilyPond is "a computer program and file format for music engraving" (quote from wikipedia). There's a LilyPond tag on stackoverflow and a LilyPond tag on the Music SE.
I recently asked a question about how to do something in LilyPond on SO here but got downvoted and another user (not the down-voter) pointed out that it is not a programming question. But it is. I've asked too on the Music SE here but I am confused. Where should such a question live on SE? Is it OK to cross-post to two relevant SE's? Why is LilyPond frowned on in SO?