Relative paths

Does anyone know of a good reference explaining relative paths. The directory structure I am currently using is as follows

Root
as
fla
swf
xml

Not complex at all.

If I’m working with a flash piece located in the “root” directory its easy. If I’m in the swf folder and want to reference an external .as file in the “as” folder, how do I ref using relative path. i.e “…/as/whatever.as” – wrong

Any help is appreciated!