So I have had a little follow-on question: how strict/forgiving are the "PM HTML recommendations", specifically with regard to whether the closing tags are required?

Closing a P element is done implicitly in the absence of closing tag, both in HTML and on PerlMonks. I've never had a problem there. On the other hand, I've had problems omitting closing tags for table-related elements on PerlMonks, even though it was valid HTML.