The ball in this example bounces off the edges of the stage. The ball actually bounces off the box movieclip that takes up the whole stage in the background. If you open up this swf in a separate window and resize the stage, the background with stretch with the new size but the ball will remain the same and will maintain its bouncing off the edges of the stage (not being confined to the same area - instead being confined to the size of the stage itself).
