code: function(e) {
          var delta = this.delta;
          this.delta = 0;
          
          if (delta) {
              e.xy = this.map.events.getMousePosition(e);
              if (delta < 0) {
                  this.callback("down",
                      [e, this.cumulative ? Math.max(-this.maxDelta, delta) : -1]);
              } else {
                  this.callback("up",
                      [e, this.cumulative ? Math.min(this.maxDelta, delta) : 1]);
              }
          }
      }
docs: Method: wheelZoom
  Given the wheel event, we carry out the appropriate zooming in or out,
  based on the 'wheelDelta' or 'detail' property of the event.
  
  Parameters:
  e - {Event}