A particle restriction whose restricting element has a union-typed base element
was checked by structural member subsetting: PureXML accepted a separately
declared union whenever its members were a subset of the base union's. That is
not the spec's derivation relation. The NameAndTypeOK type clause (XSD 1.0
section 3.9.6) requires the restricting element's type to be validly derived
from the base element's type per Type Derivation OK (Simple), cos-st-derived-ok.
The restricting type is now valid over a union base only if it is the base
type, derives from it through a declared restriction chain, or (clause 2.2.4)
validly derives from one of the union's member types. Scoped to the
element-restriction path, so no attribute or simple-type derivation check moved.
Catches particlesIk011 (a fresh union(integer) is not a restriction of
union(integer, string)): XSTS invalid-schemas-accepted 9 to 8, valid-schemas-
rejected held at 0 over the full corpus (the cardinal no-over-rejection check).
Disclosed: particlesIk025/Ik027, where the restricting type derives from a
union member, are accepted per cos-st-derived-ok 2.2.4, a contested reading
their XSTS invalid expectation does not share. An in-repo test that asserted
the old structural-subset behavior is corrected.
XSD 1.0 cos-particle-restrict NameAndTypeOK.2.2: when a complexContent
restriction narrows an element, the element's type must be validly derived
from the base element's type EXCLUDING extension (and list/union), i.e. by
restriction only. The element-type check followed the derivation chain
regardless of method, so a type derived from the base by extension was wrongly
accepted as a valid restriction (corpus particlesIj008).
Add typeDerivesByRestriction (as typeDerivesOrEqual, but the user-declared
chain is followed across restriction steps only; an extension step breaks the
walk) and use it on the non-union fall-through of elementTypeRestrictionOK.
The shared typeDerivesOrEqual is untouched, so substitution-group validity
(where extension is legal) is unaffected. Built-in lattice and union-base
derivation are unchanged, so valid restrictions, including the union-member
restriction addB150, still compile.
XSTS invalid-schemas-accepted 37 -> 36; valid-schemas-rejected held at 0
across all 14383 groups. Union-base (Ik011/Ik025/Ik027) and substitution-group
(V020) cases need the by-name union-member and ref-resolution clauses and stay
deferred.
