-Sent when someone changes their nickname. The 'old_client_entry' includes
-the old nickname and the 'new_client_entry' includes the new nickname.
-Application must understand that the 'old_client_entry' pointer becomes
-invalid after returning from the function. Note that this notify is not
-delivered when user changes its own nickname.
+Sent when someone changes their nickname. The 'client_entry' is the client
+whose nickname is changed. The `old_nickname' is the old nickname and the
+`new_nickname' is the new nickname. It has been already updated into the
+`client_entry'.