By changing the values in the form, you can generate a document with specific Expires and Last-Modified headers. The RFC field refers to the format used to represent time. RFC1123 is preferred but some programs generate RFC850. Agents and servers should understand both formats.
Apache will cache the URLs generated by this form; however, Squid cache will not by default (you must comment out "http_stop ?" in squid.conf). Alternatively, you can encode the arguments to the script in PATH_INFO instead of QUERY_STRING, like this:
More on Proxy Cacheing Servers
what is a cache (Netscape)