One of the lectures in my courses had me asking the following question: Is HTML5 a subset of SGML?
I did a little googling. Here are the links I found most relevant. Maybe someday I will write my own opinion on the topic... The short answer is that HTML5 became an abstract language with two modes of instantiation. One is XML valid (and hence SGML), the other is not SGML valid.
- https://www.w3.org/2008/Talks/04-24-smith/index.html
- https://mathiasbynens.be/notes/xhtml5
- https://html.spec.whatwg.org/#html-vs-xhtml
- https://stackoverflow.com/questions/5558502/is-html5-valid-xml/39560454#39560454
- https://stackoverflow.com/questions/8460993/p-end-tag-p-is-not-needed-in-html
- https://stackoverflow.com/questions/1946426/html-5-is-it-br-br-or-br
- https://stackoverflow.com/questions/5558502/is-html5-valid-xml