XM (standing for eXtended Module) is a popular module music file format, that was introduced in 1994 in FastTracker2 by Triton demo group. Akin to MOD files, it bundles both digital samples (instruments) and instructions on which note to play at what time (patterns), which provides good audio quality with relatively small file size. Audio is reproducible without relying on the sound of particular hardware samplers or synths.
This page hosts a formal specification of Extended Module using Kaitai Struct. This specification can be automatically translated into a variety of programming languages to get a parsing library.