MMLX is a music programming language used to make NES Chiptunes. It extends from Music Macro Language: http://en.wikipedia.org/wiki/Music_Macro_Language

It is short for MML eXtended. Everything written in MML is valid in MMLX, but there are additional features.

If you are familiar with web programming, MMLX is to MML what SASS is to CSS

For a getting started tutorial check out:
https://github.com/ccampbell/mmlx/wiki/Getting-Started

For complete documentation:
https://github.com/ccampbell/mmlx/wiki/Documentation

via ccampbell/mmlx – GitHub.