Deepen DTD processing in the doctype scanner:
- Conditional sections are processed, not skipped: INCLUDE sections have
their declarations scanned, IGNORE sections are discarded, the keyword
may be a parameter-entity reference, and nested sections are handled.
- <!NOTATION> declarations are parsed and stored on DocumentType.
- Unparsed entities (<!ENTITY ... NDATA n>) are parsed and stored with
their notation, distinct from general entities.
- External parameter entities are loaded through the injected resolver so
their declarations expand; the default refusing resolver loads nothing,
keeping XXE closed.
- NOTATION attributes are a distinct type, validated against the declared
notations (value must be listed and the notation declared).
Tracking unparsed entities also lets ENTITY/ENTITIES attribute values be
validated against the declared NDATA entities, closing the gap left when
#73 could only check name syntax.
Closes#72
Slice 3 of #92. The DTD validator's imperative walk becomes declared Validation
values over a DTDSchema document:
- DTDSchema is now just the schema (content models + attribute declarations) and
serves as the rules' Document context; its validate/walk methods are gone.
- contentModel and attributeDeclarations are Validation<Element, DTDSchema>, so
every content-model and attribute violation is now located by coding path
("... at path: r/a"). undeclaredElement is added only in strict mode.
- identifierIntegrity is a Validation<Node, DTDSchema> gated to the root, doing
the document-wide ID-uniqueness and IDREF-resolution checks in one pass.
- DTD.validator(strict:) assembles the rule set; validateAgainstInternalDTD runs
it and returns [ValidationError] instead of [Issue].
A new test pins the located result. Schema (XSD) and Schematron validators still
use Issue and migrate in the following slices.
