code: function(wheelDelta, timeStamp, pageX, pageY) {
  
  			var self = this;
  			var change = wheelDelta > 0 ? 0.97 : 1.03;
  
  			return self.zoomTo(self.__zoomLevel * change, false, pageX - self.__clientLeft, pageY - self.__clientTop);
  
  		}
docs: /*
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  EVENT CALLBACKS
  ---------------------------------------------------------------------------
   
  Mouse wheel handler for zooming support