There are Perl module names such as Moose and MooseX or DBI and DBIx or Catalyst and CatalystX or Mojo and MojoX, PPI and PPIx, etc.
What does the suffix X mean there?
eXtension, to a large extent. This is just an agreement on adding functions to the code base without topping in the real namespace or breaking the rules. DBIx means that it is connected but not part of the DBI , for example.