code: function initialize() {
        if (!rgCtrl) {
          throw 'RadioButton: No RadioGroupController could be found.';
        }
  
        rgCtrl.add(render);
        attr.$observe('value', render);
  
        element
          .on('click', listener)
          .on('$destroy', function() {
            rgCtrl.remove(render);
          });
      }
docs: Initializes the component.