Third W3C-suite strictness pass: DTDContentModelGrammar validates each
element declaration's content specification against the XML 1.0 grammar
(productions 46-51) at DTD scan time, EMPTY/ANY, Mixed (with #PCDATA first,
names only, the trailing * required with alternatives, no nesting), and
children (one connector per group, quantifiers bound directly to their
particle, balanced parentheses, no empty groups, no SGML leftovers like
'- -', 'O O', '&' connectors, or inclusion/exclusion suffixes). The element
declaration also requires whitespace after <!ELEMENT and after the name. The
lenient ContentModelParser still drives validation behavior; this is a
well-formedness gate. not-wf/sa: 129/186 rejected (from 109); valid/sa
unchanged; zero false positives across all 846 suite tests; baseline rebased
to the exact 57 remaining (declaration-grammar details and the entity
replacement-text class).
Part of #120, #105