sub serialize {
  my $writer=shift;
  my $tag=shift;
  my $value=shift;
  if ($tag eq 0) {
    $writer->characters($value);
  } else {
    $writer->startTag($tag,%{$value->[0]});
    shift(@$value);
    while (@$value) {
      my $t=shift(@$value);
      my $v=shift(@$value);
      serialize($writer,$t,$v);
    }
    $writer->endTag();
  }
}