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.
Mihaela Mihaljevic
89f8ccc95a