loprog / hiprog
The region plays when the MIDI program number is between loprog and hiprog. MIDI program numbers in the General MIDI spec ranged from 0 to 127 but were often displayed externally as 1 to 128. This uses the 0 to 127 range. Default is loprog=0 hiprog=127. By default, most DAWs seem to have the program number set to 0, so setting loprog higher than 0 without sending program change messages results in no sound.
loprog=0 hiprog=0 loprog=1 hiprog=1 loprog=10 hiprog=12