#!/usr/bin/env perl 
use strict;
use warnings;
use XML::LibXML;

my $dom = XML::LibXML->load_xml (string => <<'EOT');
<?xml version="1.0"?>
<header>
   <idset id="100">
      <a>item_a</a>
      <b>item_b</b>
   </idset>
</header>
EOT

my $object11 = $dom->findnodes ('/header/idset');
my @attrs    = $object11->shift->attributes;

print "@attrs\n";