BIDI_NOTIFY_PORT_RELEASED(22h) notifies the port driver that the port is no longer selected in a print object. The spooler sends this command to notify the port driver that the output port is no longer connected to a print queue. BIDI_NOTIFY_PORT_SELECTED(21h) allows the port driver to know that the spooler will not be sending print jobs to this printer.

The port driver should not assume that no job can be sent to this port, because an application can still print OD_DIRECT to this port. BIDI_NOTIFY_PORT_RELEASED(22h) can assist the port driver in determining the type of connection necessary for the printer.