A selector/field xpath in an identity constraint may name elements/attributes
with namespace-qualified name tests; every prefix used must be a declared
xmlns: prefix in scope (the implicit xml prefix excepted). identityXPathErrors,
after the existing syntax check, now resolves each name-test prefix against the
in-scope bindings (namespaceBindingsInScope, which captures the schema root and
every ancestor) and rejects an undeclared one.
An adversarial review confirmed no false positive: a prefix declared on the
schema root, any intermediate ancestor, or the selector/field element resolves
correctly; xml, the child::/attribute:: axis keywords (colon-free), prefix:*,
and inter-token whitespace are all handled.
XSTS: invalid-schemas-accepted 77 to 75 (idI010, idJ011), valid-schemas-rejected
held at 0, no other bucket moved. (Two existing xpath-syntax fixtures used an
undeclared 'ns' prefix to test name-test syntax; the test schema now declares
xmlns:ns so they exercise syntax with a bound prefix.)