is the "outstanding Client updates sequence number note", or the
"oustanding note".
-When the server processes a message from the client, it puts the
-client sequence number in the update stream (as a non-update message).
-(This is skipped if it's the same as the last client sequence number
-for that client.)
+When the server processes a message from the client and Records it, it
+puts the client sequence number in the update stream (as a non-update
+message). (This is skipped if it's the same as the last client
+sequence number for that client.)
If the echoed sequence number is equal to the client's oustanding
note, the client knows the server is up to date, and deletes the note.