Apologies for the delay; I've been sick since Monday.
I've revised PaceProfile to make it more complete, as requested.
http://www.intertwingly.net/wiki/pie/PaceProfile
The biggest change from the previous approach is that cardinality of metadata elements is specified by those elements, in the form "When present, atom:title MUST occur exactly once." Profiles only constrain what metadata elements are required in the feed.
Regards,
-- Mark Nottingham http://www.mnot.net/
