An attribute use that references a global attribute carrying a `fixed` value
constraint may not contradict it (au-props-correct.2): a `fixed` on the
reference whose value differs from the global's, or a `default` on a reference
to a fixed attribute, is invalid. A reference that omits its own value
constraint inherits the global's and stays valid.
The two `fixed` values are compared in the attribute type's value space, so a
value-equal pair written in different lexical forms (`01` for `1`) is not
flagged. The global is resolved by local name and only checked once its own
namespace matches the reference's resolved namespace, so a same-local-name
attribute imported from another namespace cannot surface as the wrong global
and contradict a valid reference.
Caught two invalid schemas: XSTS invalid-schemas-accepted 232 -> 230, no other
bucket moved.
A complex type's or attribute group's attribute-use set (flattened through
attributeGroup references) may not contain two distinct declarations with the
same name and namespace (ct-props-correct.4 / ag-props-correct.2), nor more than
one attribute whose type is or derives from xs:ID (ct-props-correct.5).
Declarations are deduplicated by the identity of their declaring node, so the
same declaration reached by two attribute-group paths (a diamond) is one use,
not a clash. Names carry their resolved namespace (form / attributeFormDefault
for locals, the prefix binding for refs), so a local attribute and a reference
to a same-local-name attribute in an imported namespace do not collide. The
check runs after named simple types are resolved, so a named user type derived
from xs:ID is recognized, not just the built-in and inline forms.
XSTS: invalid schemas accepted 505 to 495 (attQ008/009/012/013, attgD006/007/
009/017, ctM003/004 now rejected), no other bucket raised. An adversarial critic
caught a false positive on same-local-name-different-namespace (fixed by
resolving the ref namespace) and a missed named-user-ID type (fixed by ordering
the check after type resolution). Disclosed under-rejections: the set inherited
through extension is not composed in; a duplicate needing an unprefixed
reference with no default namespace is not detected.
