code: public function addMessage($message, $namespace = self::NAMESPACE_INFO)
      {
          if (!$message instanceof NotificationEntityInterface) {
              $messageText = $this->isTranslatorEnabled()
                  ? $this->getTranslator()->translate($message, $this->getTranslatorTextDomain())
                  : $message;
  
              $message = new NotificationEntity();
              $message->setNotification($messageText);
              $message->setPriority($this->namespace2priority[$namespace]);
          }
          $nEvent = new NotificationEvent();
          $nEvent->setNotification($message);
          $this->notificationListener->trigger(NotificationEvent::EVENT_NOTIFICATION_ADD, $nEvent);
  
          return $this;
      }
docs: send a message to the notification-handler
  @param $message
  @param string $namespace
  @return $this