cvc-id: when an instance omits an attribute, its default/fixed value applies, so
a defaulted or fixed xs:IDREF/xs:IDREFS must still resolve to a matching xs:ID.
The reference was recorded only for attributes physically present, so a dangling
defaulted IDREF was wrongly accepted. The supplied value is now recorded for
document-scoped ID/IDREF checking exactly as a present value would be (shared by
the tree and streaming validators, which both call validateAttributes). A
required absent attribute is still reported as missing, recordIDs is a no-op for
non-ID types, and a defaulted IDREF that does resolve stays valid. Catches
idZ012. XSTS invalid-instances-accepted 20 to 19, valid-instances-rejected held
at 0.
