The Squid developers maintain a separate site,
currently hosted at SourceForge, for experimental Squid features.
Check it out at http://devel.squid-cache.org/. There
you'll find a number of cutting-edge development
projects that haven't yet been integrated into the
official Squid code base. You can access these projects through
SourceForge's anonymous CVS server or download diff
files based on the standard releases.