I'm still reviewing the TT change. AI says some of the domintro and notes might be stale.

• source:126274, 126518, 126611, 126737 — the four domintro TypeError sentences are now wrong and should be deleted. They say: "Throws a TypeError if the node document is an XML document and a Trusted Types default policy supplied a sanitizer
  (unless Content Security Policy is report-only)." With the fall-through, an XML document skips createParserOptions entirely, so the XML path is now identical to pre-PR behavior. Concretely, XHTML document + require-trusted-types-for 'script'
  enforced + default policy {createHTML: s => s, createParserOptions: o => ({...o, sanitizer})}: documentType is "xml" → shortcut skipped → get trusted type compliant string → createHTML runs → no TypeError, contradicting the sentence. And in the
  case where it does throw (no createHTML), the cause is the ordinary sink-type mismatch, not the supplied sanitizer — that throw already happens on main today. This PR introduces no new exception in XML documents, so all four sentences describe
  behavior that doesn't exist.