This is a new library package for MusicXML in Java. It is needed by Audiveris, which I am packaging. I have committed the ebuild to java-overlay so see the URL.
James my dear, 7 years later and what do you want to do with this package?
I must admit that Audiveris isn't quite as alive as I thought it was but I used to be in contact with the developer so I may reach about to him when I get a chance to look at it. It really is unique in the free software world and I would still like to use it. The latest code still relies on proxymusic.