I still feel there's something not quite right about having instruments on the same level as roles/contributions rather than one level below. To me it seems that if an actor plays a part then their character has the same type of relationship to their role as an actor as an instrument has to a musician's role as an instrumentalist.
Source is a bit weak currently. If it's going to use a fixed vocabularly it needs at least 'other' in addition to 'unknown'. Also a little ill-defined in a way; you might have ripped it off a CD or encoded from FLAC, but where was it before that? I can see this might be useful for organising music collections though. Imalone 04:16, 4 December 2007 (PST)
Categories to be free-form?
Should category's sort attribute and the genere element be free-form or use fixed values? I think at least for the sort attribute a fixed vocabulary could be usefull. To provide a fixed, basic sorting mechanism. But what sorts of music are there? Should we use some major music publication's fixed categories?
Can they be specified as a space separated list of languages? I could not figure out from the XML specifications.
The Science of Sleep (example title) is English, so the title element should be xml:lang="eng". But how to deal with the fact that this title is also used in Scandinavian languages? It is not a Scandinavian languag, but the title is used in Scandinavian contries. So … I actually have no idea how to deal with this. Maybe implement the same specifications as used in the HTTP/1.1 specification? They use a lang;q=N,lang;q=N operator to sort multiple languages by priority.