$letter ||= '@';
next if defined $done_subfields{$letter};
my @values = $field->subfield($letter);
push @subfield_loop, {marc_subfield => $letter, marc_values => @values };
push @subfield_loop, {marc_subfield => $letter, marc_values => \@values };
$done_subfields{$letter} = 1;
}
-