my $dst_piece = $board->[$to_row][$to_col];
# White short castling (regular or Chess960 king-takes-rook)
my $dst_piece = $board->[$to_row][$to_col];
# White short castling (regular or Chess960 king-takes-rook)
my $dst_piece = $board->[$to_row][$to_col];
# Black short castling (regular or Chess960 king-takes-rook)
my $dst_piece = $board->[$to_row][$to_col];
# Black short castling (regular or Chess960 king-takes-rook)