diff --git a/core/lib/Drupal/Core/Messenger/MessengerInterface.php b/core/lib/Drupal/Core/Messenger/MessengerInterface.php
index d9b7547..fcc5b55 100644
--- a/core/lib/Drupal/Core/Messenger/MessengerInterface.php
+++ b/core/lib/Drupal/Core/Messenger/MessengerInterface.php
@@ -4,6 +4,9 @@
 
 /**
  * Stores messages send out to the user on the page.
+ *
+ * Examples for these messages are for example that a specific content got
+ * saved.
  */
 interface MessengerInterface {
 
diff --git a/core/lib/Drupal/Core/Messenger/SessionMessenger.php b/core/lib/Drupal/Core/Messenger/SessionMessenger.php
index ed73152..e293fbd 100644
--- a/core/lib/Drupal/Core/Messenger/SessionMessenger.php
+++ b/core/lib/Drupal/Core/Messenger/SessionMessenger.php
@@ -8,6 +8,9 @@
 
 /**
  * Provides a session-based messenger.
+ *
+ * This is the default implementation used by Drupal to store message to the
+ * user.
  */
 class SessionMessenger implements MessengerInterface {