code: function (evt) {
          var controls = this.controls,
              button = evt.buttonElement;
          for (var i=controls.length-1; i>=0; --i) {
              if (controls[i].panel_div === button) {
                  this.activateControl(controls[i]);
                  break;
              }
          }
      }
docs: Method: onButtonClick
  
  Parameters:
  evt - {Event}