diff --git a/core/lib/Drupal/Core/Theme/ThemeNegotiatorInterface.php b/core/lib/Drupal/Core/Theme/ThemeNegotiatorInterface.php
index 2838569..1050cd4 100644
--- a/core/lib/Drupal/Core/Theme/ThemeNegotiatorInterface.php
+++ b/core/lib/Drupal/Core/Theme/ThemeNegotiatorInterface.php
@@ -12,11 +12,9 @@
 /**
  * Defines an interface for classes which determine the active theme.
  *
- * To set the active theme, create a new service tagged with 'theme_negotiator'
- * (see user.services.yml for an example). The only methods this service needs
- * to implement are applies and determineActiveTheme. Return the name of the
- * theme, or NULL if other negotiators like the configured default one should
- * kick in instead.
+ * To set the active theme, create a new service tagged with 'theme_negotiator',
+ * (this service uses the class \Drupal\user\Theme\AdminNegotiator). The service
+ * class needs to implement \Drupal\Core\Theme\ThemeNegotiatorInterface.
  *
  * If you are setting a theme which is closely tied to the functionality of a
  * particular page or set of pages (such that the page might not function
@@ -47,7 +45,8 @@ public function applies(RouteMatchInterface $route_match);
    *   The current route match object.
    *
    * @return string|null
-   *   Returns the active theme name, else return NULL.
+   *   Return the name of the theme, or NULL if other negotiators like the
+   *   configured default one should kick in instead.
    */
   public function determineActiveTheme(RouteMatchInterface $route_match);