I think they're broken. On #Windows anyway. As far as my logic understands, any running program should not know that they even exist. But #xampp can tell. Or at least, I think Windows is just feeding it directories as if it could tell. This is a little rough to explain.
Say we have a #PHP file on an #Apache server in a directory, but that directory is actually what Windows calls a junction (A type of symbolic link). If I 'require' another php file with a relative link like '../', where is the server going to look?
My first guess? The directory above the junction. It took me nearly an hour to determine that it was looking in the directory above the TARGET of the junction. Maybe that's the way that should work for some reason. But I do not know what that reason is. If Windows had any kind of proper sandboxing, it'd be a major security hole.
I do seem to be good at finding the #CornerCases.