Flash advice needed: How do you position elements based on the screensize?

Hello.

Quite often I see flash websites that stretch a full 100% of width and height of my browser window. They do so without changing the size of any elements (12 pt type stays 12pt) and the elements position and re-position themselves automatically depending on your screensize as if the formula is something like:
” position x = 100% of screen – 50px. ” that way whatever the element would always even after resizing be 50px off from the right side of the edge of the browser window.
The same is done with top and bottom, a loading bar for example that is always at the very bottom or a menu that runs along top.

I cannot figure out how it’s done, as any ‘publish’ setting will simply stretch the swf to 100% either by distorting the dimensions or by ‘enlarging’ the elements.

Any link to tutorials and advice would be much appreciated.
M.