From New features in Apache 2.0:
Apache modules may now be written as filters which act on the stream of content as it is delivered to or from the server. This allows, for example, the
output of CGI scripts to be parsed for Server Side Include directive by mod_include.
There's more on Filters in the Apache 2 Documentation.
I haven't used this stuff, just heard about it
at Apachecon Europe. Apache 2 is still alpha.
Brigitte 'I never met a chocolate I didnt like' Jellinek