Perldoc

perldoc is part of the perl distribution and allow you look up Perl documentation in POD format.

Examples:

perldoc /opt/rt3/lib/RT/Ticket.pm
perldoc /opt/rt3/lib/RT/Transaction_Overlay.pm
perldoc DBI
perldoc DBIx::SearchBuilder
perldoc DBIx::SearchBuilder::Record

RT::!OnlineDocs

The RT::OnlineDocs extension is available via CPAN. This extension allow viewing of the API documentation from with RT by users with SuperUser rights.