See also the MEI project at <a href="http://music-encoding.org" rel="nofollow">http://music-encoding.org</a>. Not quite the same thing, but still noteworthy. It's an attempt to provide a parallel to TEI (<a href="http://www.tei-c.org" rel="nofollow">http://www.tei-c.org</a>) for music notation. MEI is still under development, and they're supposedly working on some way to output notation (maybe through Lilypond; it's been a few months since I've kept up with the project).
Missing pedalling articulations, useful to pipe organ, harp... Also I didn't find any way to include registration change, important in pipe organ, harmonium, harpsichord, electroacoustic instruments and others.