/**
  * @param SiteConfig $config
  * @param SiteTree $owner
  * @param string $metadata
  *
  * @return void
  *
  */
 public function updateMetadata(SiteConfig $config, SiteTree $owner, &$metadata)
 {
     // Facebook App ID
     if ($config->FacebookAppID) {
         $metadata .= $owner->MarkupComment('Facebook Insights');
         $metadata .= $owner->MarkupFacebook('fb:app_id', $config->FacebookAppID, false);
         // Admins (if App ID)
         foreach ($config->FacebookAdmins() as $admin) {
             if ($admin->FacebookProfileID) {
                 $metadata .= $owner->MarkupFacebook('fb:admins', $admin->FacebookProfileID, false);
             }
         }
     }
 }