This module contains several data tables useful in various kinds of
HTML parsing operations.

Note that all tag names used are lowercase.

In the following documentation, a "hashset" is a hash being used as a
set -- the hash conveys that its keys are there, and the actual values
associated with the keys are not significant.  (But what values are
there, are always true.)

WWW: https://metacpan.org/release/HTML-Tagset