Complete the DTD attribute handling found in the audit:
- Default and #FIXED attribute values are applied to the parsed tree.
parseApplyingInternalDTDDefaults returns a tree where every element
carries the attributes its <!ATTLIST> defaults, so an editor sees the
same effective attributes a validating processor would.
- NMTOKEN, NMTOKENS, ENTITY, ENTITIES are validated: NMTOKEN(S) must be
XML name tokens, ENTITY/ENTITIES must be XML names. Previously all fell
through to unconstrained CDATA.
- DTD default values are normalized per XML 1.0: character and predefined
entity references are expanded, literal whitespace becomes a space, and
non-CDATA values are collapsed and trimmed.
ENTITY/ENTITIES check name syntax only; that the named entity is a
declared unparsed entity is not verified, since NDATA entity tracking is
not yet modeled.
Closes#73
Add PureXML.Parsing.XMLCharacter as the single source of truth for character
classes, implementing the exact XML 1.0 (Fifth Edition) Char, NameStartChar, and
NameChar productions as public scalar predicates, plus isValidName. The scanner's
name recognition now delegates to these exact ranges (replacing a loose isLetter
check) and handles precomposed and combining-mark names. Closes#35.
Reimplemented from the XML grammar; no upstream code copied. 4 tests; 98 total.
