After a discussion with Joseph today, we agreed that the core XDI graph model rules he is trying to make sure are fully captured in the
ABNF should also be written down as classic RFC style MUST/MAY/SHOULD rule form.
We have done this in several earlier iterations, but to bring this all together and make it consistent with our revised syntax, I have drafted this new proposal page:
Please read it over and post any feedback or corrections to the list (or make them directly to the page).