SWISS::OXs
SWISS::OXs represents the OX lines within an SWISS-PROT + TrEMBL entry as specified in the user manual http://www.expasy.org/sprot/userman.html . The OXs object is a container object which holds a list of SWISS::OX objects for each currently permitted taxonomic resource.
SWISS::BaseClass.pm
NCBI_TaxIDA ListBase object which holds a list of tax ids.
  $taxid = new SWISS::OX;
  $taxid->text('1234');
  $entry->OXs->NCBI_TaxID()->add($taxid);
  foreach my $taxid ($entry->OXs->NCBI_TaxID()->elements()) {
    print $taxid->text, "\n";
  }