  *  you must extend <code>LayoutBase</code> or one of its subclasses.
  *
  *  <p>At minimum, subclasses must implement the <code>updateDisplayList()</code>
- *  method, which positions and sizes the target GroupBase's elements, and 
- *  the <code>measure()</code> method, which calculates the target's default
- *  size.</p>
+ *  method, which positions and sizes the <code>target</code> GroupBase's elements, and 
+ *  the <code>measure()</code> method, which calculates the default
+ *  size of the <code>target</code>.</p>
  *
  *  <p>Subclasses may override methods like <code>getElementBoundsAboveScrollRect()</code>
  *  and <code>getElementBoundsBelowScrollRect()</code> to customize the way 

        if (!scrollRect)
            return null;

		// Make sure that the drag-scrolling regions don't overlap 
		var x:Number = dropLocation.dropPoint.x;
		var y:Number = dropLocation.dropPoint.y;
		
		var horizontalRegionSize:Number = Math.min(dragScrollRegionSizeHorizontal, layoutTarget.width/2);
		var verticalRegionSize:Number = Math.min(dragScrollRegionSizeVertical, layoutTarget.height/2);
		// Return early if the mouse is outside of the drag-scroll region.
		if (scrollRect.left + horizontalRegionSize < x && x < scrollRect.right - horizontalRegionSize &&
			scrollRect.top + verticalRegionSize < y && y < scrollRect.bottom - verticalRegionSize )
			return null;
		
		if (timeElapsed < dragScrollInitialDelay)
			return new Point(); // Return zero point to continue firing events, but not actually scroll.
		timeElapsed -= dragScrollInitialDelay;

        // Speedup based on time elapsed
        var timeSpeedUp:Number = Math.min(timeElapsed, 2000) / 2000;

    private var _dragScrollDelta:Point;
    private var _dragScrollEvent:DragEvent;
    mx_internal var dragScrollRegionSizeHorizontal:Number = 20;
    mx_internal var dragScrollRegionSizeVertical:Number = 20;
    mx_internal var dragScrollSpeed:Number = 5;
    mx_internal var dragScrollInitialDelay:int = 250;
    mx_internal var dragScrollInterval:int = 32;
    mx_internal var dragScrollHidesIndicator:Boolean = false;
    
