code: function(pos) {
          var p = pos || Dom.getXY(this.getEl());
  
          this.deltaSetXY = null;
  
          this.startPageX = p[0];
          this.startPageY = p[1];
      }
docs: Sets the start position of the element.  This is set when the obj
  is initialized, the reset when a drag is started.
  @method setStartPosition
  @param pos current position (from previous lookup)
  @private