code: function(parentPos) {
          var myPos = YAHOO.util.Dom.getXY(this.getEl()),
              ppos  = parentPos || YAHOO.util.Dom.getXY(this.parentElId);
  
          return [ (myPos[0] - ppos[0]), (myPos[1] - ppos[1]) ];
      }
docs: Returns the difference between the location of the thumb and its parent.
  @method getOffsetFromParent
  @param {[int, int]} parentPos Optionally accepts the position of the parent
  @type [int, int]