how to detect referering url?

Mar 12, 2008 at 8:58 PM
Can anyone tell me how to detect the referring url on a facebook page?

When I look at $_SERVER'HTTP_REFERER'; I get nothing back. From what I've
read, it's because in the world of FBML, the referer is Facebook itself since it
has to parse the code first.

If I have a facebook page that can be linked to from an outside site, and I want
to determine what that site it, how can I go about doing that?