#247 rejects an unescaped [ inside a regex character class, which closes the
W3C-settled invalid cases (RegexTest_993/1477) but also rejects siblings the MS
suite marks valid (([[:]+), ([[=]+), ([[.]+), RegexTest_989/990/991/1473-1475,
and the space-bearing subtraction [a - c - [ b ] ]+, 479/480). Those entries
are W3C-queried (status="queried", Bugzilla #4118) because the "valid" marking
contradicts the Appendix F grammar (SingleCharNoEsc excludes [); the suite's
settled position (993/1477) agrees with rejecting, so PureXML follows the
grammar. The queried siblings are excluded from the XSTS conformance gate, so
this is not a counted false positive.
This was shipped in #247 without surfacing the contested nature. Document the
reasoning at the error case and in the changelog so the spec-strict choice is
explicit, not silent. No behaviour change.