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@@ -200,3 +200,7 @@ It's a NIP-51-like list of pubkeys that are members of the group. Relays might c
   ]
 }
 ```
+
+## Storing the list of groups a user belongs to
+
+A definition for kind `10009` was included in [NIP-51](51.md) that allows clients to store the list of groups a user wants to remember being in.