Notes a cursor (a cursor frame or a poll cursor) and returns a new point, if any.
A cursor says that nothing undelivered lies at or below seq; it never settles an event
that was delivered and is still open, so a cursor equal to the seq of such an event
changes nothing.
The cursor.
The new acknowledgement point, or undefined.
Notes a delivered event.
Its seq.
Starts over after a (re)connect.
The server delivers again from its stored cursor, which a server restart may have set back (04 15.2 point 4), so the window forgets its own point and acknowledges again.
Notes a settled event or cursor and returns a new acknowledgement point, if any.
The settled seq (a cursor counts as delivered and settled).
The new highest seq up to which everything delivered is settled, or undefined
when the point did not move.
Tracks delivered and settled
seqvalues and computes the acknowledgement point.