Which also happens to be the definition the w3c xhtml 1.0 spec. You can choose to think that's quirky, please don't attribute it to me. Except that the number

Which also happens to be the definition the w3c xhtml 1.0 spec. You can choose to think that's quirky, please don't attribute it to me. Except that the number of people who actually implemented valid, well-formed, properly-served XHTML Strict -- of any version -- in compliance with all the relevant specifications is at best vanishingly tiny. XHTML Transitional was tag soup. Your retort further up about many sites serving invalid HTML5 actually works against you, since HTML5 explicitly has a forgiving parsing model, while XHTML is explicitly "every error is a fatal error". If browsers had enforced the XHTML approach on every document using an XHTML DOCTYPE, we would have seen the death of XHTML much earlier. This is why people say XHTML was never really adopted -- many people certainly put a "/>" to close their empty elements, and stuck an XML prolog and an XHTML DOCTYPE up at the top, but surveys like the infamous "XHTML 100" showed that next to nobody actually adopted XHTML in a manner compliant with the relevant standards. And I say this as someone who, way back in the early 00's, was serving valid, well-formed XHTML as application/xhtml+xml. XHTML was a terrible approach, and the W3C process was dragging farther and farther from practicality at every revision (remember XHTML 2.0?).