code: function() {
          if (this.map) {
              this.map.events.unregister("buttonclick", this, this.onButtonClick);
          }
          OpenLayers.Control.prototype.destroy.apply(this, arguments);
          for (var ctl, i = this.controls.length - 1; i >= 0; i--) {
              ctl = this.controls[i];
              if (ctl.events) {
                  ctl.events.un({
                      activate: this.iconOn,
                      deactivate: this.iconOff
                  });
              }
              ctl.panel_div = null;
          }
          this.activeState = null;
      }
docs: APIMethod: destroy