Document MuseScore schema

[infojunkie]

...ideally using XSD and use that to validate output MSCX files instead of invoking the mscore executable.

[infojunkie]

One crazy idea is to use an LLM to analyze the 1000s of MSCX files in the MuseScore repo, to produce an XSD that matches them all. It would also be great to produce some invalid MSCX files to ensure those are not matched.

find -name '*.mscx' | while read "f"; do cat "$f" >> all-the-musescore-files.mscx; done

[infojunkie]

I fed the MSCXs to XMLSpy and got the attached XSD. Some areas need massaging:

• The software was too eager to create choice elements where plain strings are expected
• It got severely confused by all the combinations of Note sub-elements