MIDI: Note On - Play
The region will be played when the specified note on message is received and will play for the full length of the region.

MIDI: Note On - Play / Note Off - Stop
The region will be played when the specified note on message is received and will stop when the full region is played or the specified Note Off message is received.

MIDI: Note On - Queue / Note Off - Play
The region will be queued for play when the specified note on message is received and will play when the corresponding Note Off message is received. This is used to reduce the time between receiving a trigger and playing a region.