This module lets you stack handlers so that the next one will handle
or "filter" the output of previous one.

From README:
    When you've got this module, you can use the same handler both as a
    stand-alone handler, and as an element in a chain. Just make sure that
    whenever you're chaining, all the handlers in the chain are "Filter-
    aware," i.e. they each call $r->filter_register() exactly once, before
    they start printing to STDOUT. There should be almost no overhead for
    doing this when there's only one element in the chain.

    Currently the following public modules are Filter-aware.

     Apache::Registry (using Apache::RegistryFilter, included here)
     Apache::SSI
     Apache::ASP
     HTML::Mason
     Apache::SimpleReplace

WWW: WWW: http://search.cpan.org/dist/Apache-Filter/

-- Alex Kapranoff <kapr@crosswinds.net>