Man pages matching name www::opensearch::agent in section 3pm:

WWW::OpenSearch::Agent.3pm.en	debian 10 / libwww-opensearch-perl
WWW::OpenSearch::Agent.3pm.en	debian 11 / libwww-opensearch-perl
WWW::OpenSearch::Agent.3pm.en	debian 12 / libwww-opensearch-perl