code: function(target) {
          this.target = target;
          for (var i=this.events.length-1; i>=0; --i) {
              this.target.register(this.events[i], this, this.buttonClick, {
                  extension: true
              });
          }
      }
docs: Property: startEvt
  {Event} The event that started the click sequence
   
  Constructor: OpenLayers.Events.buttonclick
  Construct a buttonclick event type. Applications are not supposed to
  create instances of this class - they are created on demand by
  <OpenLayers.Events> instances.
  
  Parameters:
  target - {<OpenLayers.Events>} The events instance that the buttonclick
  event will be triggered on.