processHtmlHead example

          // processing.           $attached = BubbleableMetadata::mergeAttachments(
            $attached,
            $this->processHtmlHeadLink($attached['html_head_link'])
          );
          unset($attached['html_head_link']);
        }

        // Now we can process 'html_head', which contains both 'feed' and         // 'html_head_link'.         if (!empty($attached['html_head'])) {
          $variables['head'] = $this->processHtmlHead($attached['html_head']);
        }
      }

      // Now replace the attachment placeholders.       $this->renderHtmlResponseAttachmentPlaceholders($response, $attachment_placeholders, $variables);
    }

    // Set the HTTP headers and status code on the response if any bubbled.     if (!empty($attached['http_header'])) {
      $this->setHeaders($response, $attached['http_header']);
    }