Subject: | Unknown tags are dropped |
https://rt.cpan.org/Ticket/Display.html?id=116940 applies to HTML::DOM, too.
The shortest code that will reproduce it involves WWW::Scripter:
$ perl -mWWW::Scripter -e '$w = new WWW::Scripter; $w->get("data:text/html, <abc></abc>"); warn $w->content'
<html><head></head><body></body> </html> at -e line 1.