How do I reference MovieClips on the Main Timeline from inside a class?

I’ve been programming with AS2 for a few years and I just made the switch to AS3. I’m hoping there is an easy solution to this problem.

I have a class ‘Actor’ (extends MovieClip) that needs to hitTestPoint on a nested MovieClip ‘root.World.walls’ in a function moveRight(). The line of code looks like this:
…while (MovieClip(root).World.walls.hitTestPoint(pnt.x, pnt.y, true)) {…

But I keep getting various errors when I try different solutions.

Does anyone know a way to fix this?