I'm scratching my head over this and hope you can point out the mistake I'm making here. Essentially I'm trying to parse a very large XML file (~600Mb) chunk-by-chunk using XML::Twig and trying to extract relevant information. I find that I cannot get value of an attribute inside an element using findvalue. XML snippet and code below. Thanks for your help!

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<ReleaseSet Dated="2014-02-11" Type="full">
<ClinVarSet ID="176987">
  <RecordStatus>current</RecordStatus>
  <Title>Single allele AND Benign familial neonatal seizures 1</Title>
  <ReferenceClinVarAssertion>
    <ClinVarAccession Acc="RCV000020962" Version="1" Type="RCV" DateUp
+dated="2013-05-06"/>
   </ReferenceClinVarAssertion>
 </ClinVarSet>
</ReleaseSet>
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And the perl bit

#!/usr/bin/perl

use strict;
use warnings;
use XML::Twig;
use Data::Dumper;

my $twig= XML::Twig::XPath->new( 
                twig_handlers => { ClinVarSet => \&ClinVar },
                pretty_print => 'indented' 
                       );                        

$twig->parsefile($file);
$twig->dispose;


sub ClinVar {
  my( $twig, $Clin)= @_;     
  my $ClinVarSetID  = $Clin->{'att'}->{'ID'};    
  my $status = $Clin->first_child('RecordStatus')->text;
  my $Accession = $Clin->findvalue('./ReferenceClinVarAssertion/ClinVa
+rAccession[@Acc]');
  
 print "ID: $ClinVarSetID\tStatus: $status\tAccession: $Accession\n";
 
}
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I get the first two values $ClinVarSetID and $status but I cannot get the value of the attribute 'Acc' using the XPath