Earlier this week, Recordare released a new Beta 3 version of the MusicXML 3.0 format. You can download everything from the zip file at:
Beta 3 includes several new features and improvements based on our implementation experiences to date, including a more flexible way to map MusicXML’s instrument sound IDs to an application’s or library’s sound IDs. There are also improvements in ornamentation, notehead shapes, and indicating a principal voice.
The stylesheet for converting from MusicXML 3.0 to 2.0 files summarizes the new language features in code form:
The MusicXML mailing list (www.recordare.com/musicxml/mailing-list) is the main place for discussing MusicXML 3.0. But please comment here or email feedback privately if you prefer.