What does the `X` suffix mean in namespaces?

There are Perl module names like Moose and MooseX or DBI and DBIx or Catalyst and CatalystX or Mojo and MojoX or PPI and PP开发者_如何学CIx, etc.

What does the X suffix mean there?

---

eXtension, pretty much. It is just a convention to add features to a code base without stomping on the actual namespace or trespassing. DBIx means it's related to but not a part of DBI, for example.