code: public function run()
      {
          if (($exception = Yii::$app->getErrorHandler()->exception) === null) {
              return '';
          }
  
          if ($exception instanceof \HttpException) {
              $code = $exception->statusCode;
          } else {
              $code = $exception->getCode();
          }
  
          if ($exception instanceof Exception) {
              $name = $exception->getName();
          } else {
              $name = $this->defaultName ?: Yii::t('yii', 'Error');
          }
  
          if ($code) {
              $name .= " (#$code)";
          }
  
          if ($exception instanceof UserException) {
              $message = $exception->getMessage();
          } else {
              $message = $this->defaultMessage ?: Yii::t('yii', 'An internal server error occurred.');
          }
  
  
          if (Yii::$app->getRequest()->getIsAjax()) {
              $rr = new RequestResponse();
  
              $rr->success = false;
              $rr->message = "$name: $message";
  
              return (array)$rr;
          } else {
              if (\Yii::$app->user->can(CmsManager::PERMISSION_ADMIN_ACCESS)) {
                  $this->controller->layout = \Yii::$app->cms->moduleAdmin->layout;
                  return $this->controller->render('@app/views/error/error', [
                      'message' => nl2br(Html::encode($message))
                  ]);
              } else {
                  $this->controller->layout = '@app/views/layouts/unauthorized';
  
                  return $this->controller->render('@app/views/error/unauthorized-403', [
                      'message' => nl2br(Html::encode($message))
                  ]);
              }
          }
      }
docs: Runs the action
  
  @return string result content