XML: How to require either or both of two child elements, but prevent both missing?

[Nozomi Ytow]

rousse> I guess you're thinking of making A and B member of Child substitution group,
rousse> and requiring a sequence of 1 to 2 Child element in parent ?

Yes, although maxOccurs was unclear for me (might be nubmer of
possible characters).

rousse> It won't solve
rousse> the problem of two A or two B, as any other constraint considering child
rousse> element separatly.

Ah.  I didn't read Gregor's description as excluding multiplication of
children; is it trouble if the Parent has multiple children, Gregor?

--
James