code: public function render($uri, $renderer = 'inline', array $options = []): ?string
      {
          if (!$uri instanceof FragmentReference) {
              return $this->fragmentHandler->render($uri, $renderer, $options);
          }
  
          $config = $this->fragmentRegistry->get($uri->controller);
  
          if (null === $config) {
              throw new UnknownFragmentException(sprintf('Invalid fragment identifier "%s"', $uri->controller));
          }
  
          $this->preHandleFragment($uri, $config);
  
          $renderer = $config->getRenderer();
  
          if (!isset($this->initialized[$renderer]) && $this->renderers->has($renderer)) {
              $this->addRenderer($this->renderers->get($renderer));
              $this->initialized[$renderer] = true;
          }
  
          return parent::render($uri, $renderer, $config->getOptions());
      }
docs: {@inheritdoc}