// STEP 1
// Create _contentWidth and _contentHeight as private vars to store the initial _content dimensions.
 
_contentWidth = _content.width;
_contentHeight = _content.height;
 
 
// STEP 2
// In your resize handler, use the following code:
 
var scale:Number = 1;
if ( _contentWidth < stage.stageWidth || _contentHeight < stage.stageHeight )
{
	scale = Math.max( stage.stageHeight / _contentHeight, stage.stageWidth / _contentWidth );
}
 
 
// STEP 3
// To apply the calculated scale, use:
 
_content.width = _contentWidth * scale;
_content.height = _contentHeight * scale;