'subtotal' => { $opt{amount_field} => "sum($amount_field)" },
'subtotal_row' => [ 'Subtotal',
sub { sprintf($money, $_[0]->$amount_field) },
'subtotal' => { $opt{amount_field} => "sum($amount_field)" },
'subtotal_row' => [ 'Subtotal',
sub { sprintf($money, $_[0]->$amount_field) },