@xmlfiles = qw(file1.xml file2.xml);


foreach my $xfile (@xmlfiles)
{  

 $twig = new XML::Twig(
                         twig_roots =>  {
                        'pdb_entry/pdb_code' => \&pdb_entry,
                        'pdb_entry/total_asm' => \&pdb_entry,
                        'pdb_entry/asm_set/assembly' => \&assembly,});


    &parse_twig($xfile);
 
 }


sub parse_twig
{
   my $file = shift;
 
   if ($twig->safe_parsefile($file) == 0)
   {
      die "Failed to parse $file: $@";
   }

   my $root = $twig->root;
   my @params = $root->children('pdb_entry');
   $twig->purge;
   $twig->dispose;
}

...
 
handler code here