Man pages matching name markdent::handler::htmlfilter in section 3pm:

Markdent::Handler::HTMLFilter.3pm.en	debian 10 / libmarkdent-perl
Markdent::Handler::HTMLFilter.3pm.en	debian 11 / libmarkdent-perl
Markdent::Handler::HTMLFilter.3pm.en	debian 12 / libmarkdent-perl