An element with a default or fixed value takes that value when it appears empty,
so the empty content is valid even where the type would reject an empty string.
The constraint value, not the empty string, is validated against the type,
including any xsi:type override, so a fixed value invalid against the overriding
type is still rejected.
Validating the constraint value under xsi:type exposed a second defect: a
restriction's enumeration was unioned with the inherited enumeration, so a
derived type wrongly accepted the base's values. Enumeration now replaces on
restriction (the new set is the value space); pattern still accumulates and is
ANDed across derivation steps.
XSTS: valid instances rejected 395 to 369, invalid instances accepted 240 to
238. Baseline updated; regression tests cover empty default/fixed, present
content still validated, and the constraint value checked against an xsi:type.
Refs #147, #129.
Mihaela Mihaljevic
c9f41c387e