Closes#75, on the validation framework. XSD instance-level features:
- nillable elements: an xsi:nil="true" element is accepted (its content model is
not checked) only when the element is declared nillable and carries no content;
xsi:nil on a non-nillable element, or a nilled element with content, is a
located error.
- fixed value constraints: a present fixed attribute must equal its fixed value,
and a fixed element's text must match.
- default/fixed are parsed onto AttributeUse (per use) and collected per element
name (nillable set + value constraints), threaded through XSDContext to the
ComplexValidator.
All findings are located ValidationErrors. Collection and helper methods move to
same-file extensions to stay within type-body limits.
Add Schema.Document compiling an xs:schema into global element declarations
and a named-type table, and validate(_:) checking instance documents end to
end. The parser supports global and local element declarations, named and
inline simple and complex types, sequence/choice/all groups with occurrence,
attribute uses, simple content (restriction/extension), the full facet set,
and recursive types via named references resolved during validation. Extends
ComplexType with a typeReference case and ComplexValidator with a type table
so recursive schemas are representable.
Closes#10
Add ComplexValidator validating an element against a ComplexType: attribute
uses (required, typed, unknown-attribute rejection) and the content model
(empty, simpleContent, elementOnly, mixed). Particles compile to a Thompson
NFA over element names honoring minOccurs/maxOccurs with sequence and choice
compositors; all groups are validated order-independently by counting. Child
elements are validated recursively against their declared types.
Closes#9
