It took me years to notice, but did you catch that the answer actually subtly misinterprets what the question is asking for?

Guy (in my reading) appears to talk about matching an entire HTML document with regex. Indeed, that is not possible due to the grammars involved. But that is not what was being asked.

What was being asked is whether the individual HTML tags can be parsed via regex. And to my understanding those are very much workable, and there's no grammar capability mismatch either.

▲ tiagod an hour ago | parent [-]

I think even for single opening tags like asked there are impossible edge cases.

For example, this is perfectly valid XHTML:

    <a href="/" title="<a /> />"></a>

	▲	comex 28 minutes ago \| parent [-]
		If you already know where the start of the opening tag is, then I think a regex is capable of finding the end of that same opening tag, even in cases like yours. In that sense, it’s possible to use a regex to parse a single tag. What’s not possible is finding opening tags within a larger fragment of HTML.