Man pages matching name latexml::core::definition::register in section 3pm:

LaTeXML::Core::Definition::Register.3pm.en	debian 10 / latexml
LaTeXML::Core::Definition::Register.3pm.en	debian 11 / latexml
LaTeXML::Core::Definition::Register.3pm.en	debian 12 / latexml
LaTeXML::Core::Definition::Register.3pm.en	debian 13 / latexml