Comment by dragonwriter
5 hours ago
> There was an attempt to nail its syntax down in the pre-HTML 5 days; that's XHTML. When HTML 5 pivoted away from that, that spelled the end of these two things ever coming together.
Exactly the opposite; WHATWG “Living Standard” HTML (different releases of which were used as the basis for W3C HTML5, 5.1, and 5.2 before the W3C stopped doing that) includes an XML serialization as part of the spec, so now the HTML-in-XML is permanently in sync with and feature-matched with plain HTML.
https://html.spec.whatwg.org/multipage/xhtml.html
“Warning! Using the XML syntax is not recommended, for reasons which include the fact that there is no specification which defines the rules for how an XML parser must map a string of bytes or characters into a Document object, as well as the fact that the XML syntax is essentially unmaintained — in that, it’s not expected that any further features will ever be added to the XML syntax (even when such features have been added to the HTML syntax).”