XSD 1.0 §3.11.4 (cvc-identity-constraint.3) requires each key/keyref/unique
field to identify a node of simple type. A field that reaches an element
declared with no type (the ur-type anyType) or an inline complex type without
simple content does not, so the instance is invalid; the reference (libxml2)
rejects it identically. PureXML accepted such instances because its identity
validator could resolve a field target's type only for a global element reached
by a direct-child name, not for a local element reached through a path (the W3C
XSTS case idZ010 nests anyType fields several levels deep, e.g. a key field
./b/c where c has no type).
A compile-time pass (XSDParser.identityNonSimpleFieldKeys) resolves each field's
target element through its selector and field paths, by element-name steps, and
records the fields whose declared target is provably non-simple. The validator
rejects those at runtime unless the instance gives the node a simple type
through xsi:type, since cvc reads the node's governing type (a text-only anyType
element with xsi:type="xsd:int" is a valid field). The resolution is
conservative: any wildcard, descendant axis, predicate, ref, or named
non-builtin type leaves the field unflagged, so a valid field is never rejected.
The one residual divergence path, two same-name child elements of differing
simplicity in one inline model, is an Element-Declarations-Consistent violation
the compiler already rejects.
Verified over the full W3C XSTS corpus in release: invalid-instances-accepted
8 -> 7 (idZ010 now rejects), valid-instances-rejected held at 0 across all 14383
groups (no false positive), full suite (1837 tests), wasm, and lint all green.
An adversarial critic that read every file and probed for a false positive could
not construct one; the failure mode is under-rejection, the safe direction.
