I would like to declare files (in my case 'a' and 'i') as a promotion zone for pawns. Is that possible?
It is. Set maxPromote=0 to suppress normal promotion, and immediately after the Pawn definition line write
morph=*.......*/"/"/"/"/"/"/"/"
This declares the 1st and 9th square of the first rank to squares where Pawns will promote with chess-like choice, and then repeats that for the next 8 ranks. You might consider rotating the diagram 90-degrees, though...
It is. Set maxPromote=0 to suppress normal promotion, and immediately after the Pawn definition line write
morph=*.......*/"/"/"/"/"/"/"/"
This declares the 1st and 9th square of the first rank to squares where Pawns will promote with chess-like choice, and then repeats that for the next 8 ranks. You might consider rotating the diagram 90-degrees, though...