createElementNS() should now throw only InvalidCharacterError, not NamespaceError. Validating a qualified name should only throw InvalidCharacterError, not NamespaceError, after: https://github.com/whatwg/dom/issues/319 https://github.com/w3c/web-platform-tests/issues/5161 https://github.com/whatwg/dom/issues/423 Latest spec: https://dom.spec.whatwg.org/#validate