I see that Maretron’s DSM150, DSM200, and DSM250 displays have a J2K100 configuration setting called "NMEA 2000 Engine Instance:"; what is this?

Maretron's DSM150, DSM200, and DSM250 displays have a J2K100 configuration setting called "NMEA 2000 Engine Instance:" which is used to program the J2K100 to transmit the appropriate NMEA 2000 instance. For example, if the J2K100 is connected to the port engine, then this configuration setting would be used to program the J2K100 to transmit instance 0 since the NMEA 2000 convention states that the port engine shall be instance 0.