Man pages matching name http::oai::encapsulation in section 3pm:

HTTP::OAI::Encapsulation.3pm.en	debian 10 / libhttp-oai-perl
HTTP::OAI::Encapsulation.3pm.en	debian 11 / libhttp-oai-perl
HTTP::OAI::Encapsulation.3pm.en	debian 12 / libhttp-oai-perl