RE: keyref with empty sets

>Basically, the REC (correctly, in my view) imposes _no_
>requirements on keys if there are no hits for a keyref

From my reading of the clause below, it does seem that the content
selected by a key _must_ exist in the content, and if someone wanted to
have null keys, one would use xs:unique.

structures spec section 3.11.1:
{key) the Identity-constraint definition asserts uniqueness as for
unique. key further asserts that all selected content actually has such
tuples.



-Zafar