Reading some related questions made me think about the theoretical nature of HTML.

I'm not talking about XHTML-like code here. I'm talking about stuff like this crazy piece of markup, which is perfectly valid HTML(!)

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN">
<html<head>
<title//
<p ltr<span id=p></span</p>
</>

So given the enormous complexity that SGML injects here, is HTML a context-free language? Is it a formal language anyway? With a grammar?

What about HTML5?

I'm new to the concept of formal languages, so please bear with me. And yes, I have read the wikipedia article ;)

html grammar language-theory sgml
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