In that case, perldoc -f HTML::Parser raises the question (for me, anyway): "Is H::P the appropriate tool?
"HTML::Parser" is not a generic SGML parser. We have tried to make it able to deal with the HTML that is actually "out there", and it normally
parses as closely as possible to the way the popular web browsers do it
instead of strictly following one of the many HTML specifications from
W3C. Where there is disagreement, there is often an option that you can
enable to get the official behaviour."
But I have yet to see a browser that will treat <bold_text> as a tag, rather than simply ignoring it (and merely rendering the enclosed text without additional formatting.
Update: The doc does -- again, to me and YMMV -- suggest that you could tweak your script to deal with some of the invalid tag-like entries:
$p->strict_names( $bool )
By default, almost anything is allowed in tag and attribute names.
This is the behaviour of most popular browsers and allows us to
parse some broken tags with invalid attribute values like: