I have been peeking around a bit inside, and came along line 270:

        # This is a placeholder for a CollisionTraverser.  If someone
        # stores a CollisionTraverser pointer here, we'll traverse it
        # in the collisionLoop task.
        self.shadowTrav = 0
        self.cTrav = 0
        self.cTravStack = Stack()
        # Ditto for an AppTraverser.
        self.appTrav = 0 # <---- line 270

Does anybody know what an AppTraverser is and what it is for? I didn’t find a class with this name in direct/src or the panda/src. Just because I curious…

Umm, sounds like something vestigial from back in the very early days that never got implemented? I don’t know.