#my hack to only process worksheets matching the sheet filter
    my %sheet_filter=();
    if ($self->{sheet_filter}) {
      map {$sheet_filter{$_}} split ",", $self->{sheet_filter};
    }
    my @sheets = map {
        my $idx = $_->att('rels:id');
        if ($files->{sheets}{$idx}) {
          my $sheet = Spreadsheet::ParseExcel::Worksheet->new(
              Name     => $_->att('name'),
              _Book    => $workbook,
              _SheetNo => $idx,
          );
          $sheet->{SheetHidden} = 1 if defined $_->att('state') and $_->att('state') eq 'hidden';
          $self->_parse_sheet($sheet, $files->{sheets}{$idx});
          ($sheet)
        } else {
          ()
        }
    } grep {%sheet_filter ? defined $sheet_filter{$_->att('name')} : 1} $files->{workbook}->find_nodes('//s:sheets/s:sheet');