You are right. There is a third-party DTD that should be mostly compatible (https://sgmljs.sgml.net/docs/html5.html https://sgmljs.sgml.net/docs/html5.html).

You are right. There is a third-party DTD that should be mostly compatible (https://sgmljs.sgml.net/docs/html5.html https://sgmljs.sgml.net/docs/html5.html). In reality, HTML4 was never implemented to the letter by user agents, because people do things like putting -- inside comments.