Access MovieClip on Stage from Class

I have yet to find the right answer… I’ve created a custom class (not the document class, otherwise there would be no problem) and I want to be able to access a MovieClip that is sitting on the stage.

How? MovieClip(parent), MovieClip(root)… don’t work. What’s the proper procedure?

Also, can I pass the MovieClip from the Document Class to another custom Class?

Thank you.