Earlier quoted context omitted.
> Apparently web standards folks in the early 2000s thought the future was XML all the way down. It should have been, but just like the masses rejected LISP for its parens, the masses rejected XML for the closing tag. We could have avoided PHP and the zoo of MVC frameworks.
If only XML wasn't so damn complicated , it might have had a chance. People love to point at close tags, but there's a long list of more serious problems. External entities, namespaces within namespaces, CDATA, namespaces that confusingly look exactly like URLs, but aren't, parser vulnerabilities.
The bad smell was mostly coming from all the things inherited from SGML - CDATA, entities etc. Although I would also add that separation into elements and attributes is not a particularly convenient way to model many things; it mixes up differences that should really be orthogonal (ordered/unordered, atomic/composite etc).