Coordinates of movieclip within a movieclip?

Seemingly simple question:

I have a movieclip “scroller” within which sits a movieclip “container”.
At root level I have an instance of “scroller” which can be moved along the x axis by the user.

How do I access the x coordinates of the corresponding “container” object at any given time?

_root.scroller.container._x always gives me the same value- the value of “container_x” inside the library object of “scroller”.

Any ideas?