Movement restriction

Hi,
I’ve made a sort of sliding menu which is basically a movie clip that has a function assigned to it that if the cursor goes over a button it starts moving in a direction.


_root.right.onRollOver = function() {
    goRight = true;
};
if (goRight) {
        _root.content._x -= 10;
    }

Now, I don’t want that “content” object to slide all the way out of the screen. How can I make it stop at certain position, say x=770? Or is there any way?