LilyPond is an open-source program to produce sheet music, using a text-based input format to supply music to be printed. The extension .ly is for source files that produce output, and .ily for source files to be included rather than run on their own.
Mediawiki's Score extension allows the embedding of music, input using LilyPond notation, in wikis.
The first line of a file should be a version statement like this:
- \version "2.16.2"
The version number will vary by which LilyPond version the file is intended for.