     [Inspectable(category="General")]
 
     /**
-     *  Vertical space between rows.
+     *  Vertical space between rows, in pixels.
      *
      *  @see #horizontalGap
      *  @see #rowAlign

            for (var index:int = visibleStartIndex; index <= visibleEndIndex; index++)
                updateVirtualTileSize(target.getVirtualElementAt(index));
        }
		
		// Make sure that we always have non-NaN values in the cache, even
		// when there are no elements.
		if (isNaN(_tileWidthCached))
			_tileWidthCached = 0;
		if (isNaN(_tileHeightCached))
			_tileHeightCached = 0;
        
        if (isNaN(_columnWidth))
            _columnWidth = _tileWidthCached;


            x = column * (_columnWidth + _horizontalGap);
         
            y = emptySpaceTop + Math.round((emptySpace - height) / 2);
            // Allow 1 pixel overlap with container border
            y = Math.max(-1, Math.min(target.contentHeight - height + 1, y));
        }
        
