A complex or simple type may not derive, transitively through its base, from
itself. Such schemas were accepted. The check walks the base chain built from
each type's complexContent/simpleContent extension/restriction base (and a
simpleType's restriction base), following an edge only when the base resolves to
the schema's own target namespace.
Three exceptions keep it from over-rejecting: element content that recurses (an
element of the type's own type) is not a derivation and is not followed; a type
redefined in xs:redefine legitimately names itself as its base, so redefined
types end the chain; and the ur-types (anyType/anySimpleType/anyAtomicType,
which the schema-for-schemas bootstraps with self-referential definitions) end
the chain. The target-namespace gate prevents a local type whose base is a
same-local-name type in another namespace from being mistaken for a self-cycle
(found by an adversarial critic; the engine resolves by local name).
XSTS: invalid schemas accepted 519 to 516 (addB101, elemM003, xsd007.e now
rejected), no other bucket raised. Union/list and genuine cross-namespace
derivation cycles are a disclosed under-rejection.
Mihaela Mihaljevic
96ec9cd1e0