create_html_element implements https://dom.spec.whatwg.org/#concept-create-element and is called from the parser (via Element::create in Sink::create_element), but the HTML specification defines https://html.spec.whatwg.org/multipage/parsing.html#create-an-element-for-the-token which is used by the HTML parsing algorithms. Steps 6 and 9 are particularly relevant for dealing with #19307 (comment).