Michael Kay wrote:

>There is a very surprising rule here: when you reference two attribute
>groups and they both contain attribute wildcards, you get the intersection
>of the wildcards, not the union as you might expect.

Thank you! Is the "surprising rule" you refer to the one under 

§3.4.2-"XML Representation Summary: complexType Element Information
Item"-"Complex Type Definition with simple content Schema Component"-2.2.1 

(don't know if there is a more concise way of referring to that specific
document location)? 

Yes, I would have expected a union in the same way single attribute
definitions form a union, since my personal view up to now on
"anyAttribute" was that it's just a slightly more generalized
"attribute". Obviously, it's not, but treated quite differently. Haven't
thought on this long enough, but: are there use cases for namespace
intersections? Isn't the main concept of namespaces that they are
orthogonal and, as a consequence, the intersection of namespace
wildcards will always be empty? Ok, there is still the special
"namespaces" ##local, ##targetNamespace, ##other or ##any with which it
might yield a non-empty result.

Regards,
Christian