Village Idiot: I need a method that does not rely on the parent page to do anything special. I support my University's web services, and our content providers (CPs) are our biggest problem security-wise. Quite simply, they do things wrong. We need to determine the parent path from the include without relying on the parent file to do anything special (aside from including our file, whether directly or indirectly through nested includes). Also, I was talking about cross-server compatibility, not cross-browser; so if something would work under mod_php in apache but not with PHP running under Windows or as a CGI, for example, that's fine. A few of the sources I found mentioned minor differences between versions for things like how the directory path is handled, so I thought I'd throw that note in in case it was relevant.

delayedinsanity: I did some basic testing, too. I think I might write a test script that generates random nested include structures to test the code a bit further.