An element/attribute default/fixed value must be a valid value of its type
(Attribute/Element Locally Valid, XSD 1.0). A fixed="abc" on an xs:integer or a
default="1 2" on an xs:int was accepted because the value constraint was never
checked at compile time.
The value is now validated against its type when the type resolves to a
built-in datatype (namespace-aware: only a type in the XSD namespace),
normalising whitespace per the type so a default=" 5 " on an integer stays
valid. A named or inline user type is left to its own rules, so no valid value
constraint is rejected.
XSTS: invalid schemas accepted 638 to 621, valid schemas rejected held at 72,
instance buckets unchanged.
