code: function(funct)
  	{
  		if (funct != null)
  		{
  			var wheelHandler = function(evt)
  			{
  				// IE does not give an event object but the
  				// global event object is the mousewheel event
  				// at this point in time.
  				if (evt == null)
  				{
  					evt = window.event;
  				}
  			
  				var delta = 0;
  				
  				if (mxClient.IS_FF)
  				{
  					delta = -evt.detail / 2;
  				}
  				else
  				{
  					delta = evt.wheelDelta / 120;
  				}
  				
  				// Handles the event using the given function
  				if (delta != 0)
  				{
  					funct(evt, delta > 0);
  				}
  			};
  	
  			// Webkit has NS event API, but IE event name and details 
  			if (mxClient.IS_NS && document.documentMode == null)
  			{
  				var eventName = (mxClient.IS_SF || 	mxClient.IS_GC) ? 'mousewheel' : 'DOMMouseScroll';
  				mxEvent.addListener(window, eventName, wheelHandler);
  			}
  			else
  			{
  				mxEvent.addListener(document, 'mousewheel', wheelHandler);
  			}
  		}
  	}
docs: Function: addMouseWheelListener
  
  Installs the given function as a handler for mouse wheel events. The
  function has two arguments: the mouse event and a boolean that specifies
  if the wheel was moved up or down.
  
  This has been tested with IE 6 and 7, Firefox (all versions), Opera and
  Safari. It does currently not work on Safari for Mac.
  
  Example:
  
  (code)
  mxEvent.addMouseWheelListener(function (evt, up)
  {
  mxLog.show();
  mxLog.debug('mouseWheel: up='+up);
  });
  (end)
  
  Parameters:
  
  funct - Handler function that takes the event argument and a boolean up
  argument for the mousewheel direction.