Two more Particle Valid (Restriction) over-rejections.
A derived particle that can never contribute a child (its own maxOccurs="0", or
a group whose every member is content-free) accepts only the empty sequence, so
it validly restricts any emptiable base. Checked before the structural cases,
which previously recursed into the members of a maxOccurs="0" group and rejected
it for their own occurrences (particlesW006).
Substitution-group expansion now lists members in declaration order: the closure
walk used a popLast() stack that reversed them, so a reference to a head expanded
to choice(head, m2, m1) and an order-preserving RecurseLax restriction by
choice(m1, m2) could not map (elemZ027a). The choice/choice restriction stays
order-preserving, as the W3C suite requires (choice(b|a) is not a valid
restriction of choice(a|b), particlesT002); only the expansion order is fixed.
The expansion is shared with instance validation and the determinism check, both
order-neutral.
XSTS: valid schemas rejected 4 to 2, no other bucket raised. The pinned XSTS
baselines (never asserted under a plain swift test, the suite being opt-in) are
corrected to the measured 2/520/180/160.