[Bug 5293] Subsumption

http://www.w3.org/Bugs/Public/show_bug.cgi?id=5293





------- Comment #8 from mike@saxonica.com  2007-12-07 09:31 -------
>Whoa.  Do assertions count in subsumption or restriction checking?

You're right, the rule that says "A restricts B iff A's extent is a subset of
B's extent" applies to A and B as "content types", not to the type as a whole.

This still leaves some cases that are very hard to prove, notably cases where
one of the content types uses an all-group and the other uses a combination of
sequence and choice. For example:

B: ab?|ba?|(empty)

D: a?&b? 

It's not clear that requiring all such cases to be analyzed gives a real user
benefit.