Fit the Stage so that it only shows the things inside it!

I have asked this question some hours back and did not get my answer yet:

http://forums.adobe.com/message/5402103

To simplify my question, this is the FLA file I am talking about:
http://www.howallah.com/Mobile.fla

each flash scene is indeed divided into 3 sections based on colors (white, light grey, dark grey) as marked below :

(the Zoom is 20% to cover them all).

Section 1.   is called Stage (I know)
Section 2.   it expands automatically as you move an object outside the stage (image, movieclip etc.) and it works like a mask (I dont know the name of this section)
Section 3.   is something like "out of Scene" (I don't know the name of this section as well)

What I want to do is sort of FITTING Section 1 (Stage) to Section 2.

Exactly like the FLA sample file above.

What is that good for?? to help me only see the stuff INSIDE the stage, without any need to make a mask layer or a LARGE white layer above all layers etc.!

Anybody knows what I am talking about and having a clue please?

Regards,
   Ali