xs:complexContent. Only xs:extension is accepted.
One named complexType: a sequence, a choice, or an extension.
Children of a sequence or choice. Nested compositors and compositor
occurrence ranges are refused.
A local element declaration. Anonymous inline types are refused.
maxOccurs, defaulting to 1. unbounded is the only non-numeric
value accepted.
minOccurs, defaulting to 1.
A named simpleType that restricts a base. whiteSpace is ignored
(normalization, not a constraint). An unsupported facet fails the
compile rather than being dropped.