What's better than SGML? What would XML an HTML look like if they were based on that instead?

HTML is SGML. You know that while doctype things you're supposed to out at the start of the document? That specifies the document schema of HTML at a specific version for the current SGML doc.

	▲	andai a day ago \| parent [-]
		Yeah, hence my question. What would HTML and XML look like if they were based on this thing that's apparently superior to SGML instead of being based on SGML?