figuring out where you are in an included file

So, in the course of trying to write a factory method for a Log abstraction class that I'm working on, I figured out that it would be nice to figure out where I am on the filesystem - not just where the main script is, but where I am when I'm in an included file, like a library, that might be included from lots of different places. I figured out that this: substr(__FILE__, 0, -(strlen(basename(__FILE__)))) ... seems to give me a path, that even if it's relative, is relative to the original script, which means that I can use it in include/require lines - which is pretty much what I need, which is fine. My question is, am I crazy to depend on this, and am I missing any other way of getting the same information? -chuck