I'm an ASP.NET guy so I am clueless on helping you out, but from what I googled on it, it looks like a masking techique that's used to point particular URLS that have been passed into the server that have a pre-defined partial match to a stored string to use a different URL in place of the one that's been passed. I saw nothing in the four or five documentation pages I looked at that showed how this assignment is actually used after the masking transformation takes place. You need an Apache specific forum. I'd refer you to the one at Tek-tips.com, but I didn't get any hits on the command there either, so you may need a Usenet forum or some place where guys who eat this for breakfast hang out, as the mighty Webwench said.