%HTML::Tagset::linkElements does not include the poster attribute, which
is a link element used by the HTML5 video tag.

Result is that anything that uses that data to parse for urls (like ikiwiki
does, or like HTML::LinkExtor) will have broken handling of that attribute.

The formaction attribute is also missing. I have not exhaustively
checked for other url attributes added in HTML5.

Actually, it's worse, HTML::Tagset::linkElements{video} does not exist
at all, so it doesn't even know that <video src=..> is an url

Joey Hess wrote:

Nor does the <source> element. Guess this needs a thurough update to
support html5.