use strict;
use warnings;

use Data::Dumper;
use XML::Simple;

# The fastest existing backend for XML::Simple.
local $XML::Simple::PREFERRED_PARSER = 'XML::Parser';

my $xs = XML::Simple->new(
   NoAttr         => $ARGV[0],
   KeepRoot       => 1,
   NormaliseSpace => 1,
);

my $tree = $xs->parse_string( <<'__EOI__' );
<BILLING>
 <ACCOUNT></ACCOUNT>
 <RTN></RTN>
</BILLING>
__EOI__

print( Dumper( $tree ) );

print( $xs->XMLout( $tree ) );

##</code><code>##

$ perl a.pl 1
$VAR1 = {
          'BILLING' => {
                       'RTN' => {},
                       'ACCOUNT' => {}
                     }
        };
<BILLING>
  <ACCOUNT></ACCOUNT>
  <RTN></RTN>
</BILLING>

##</code><code>##

$ perl a.pl 0
$VAR1 = {
          'BILLING' => {
                       'RTN' => {},
                       'ACCOUNT' => {}
                     }
        };
<BILLING>
  <ACCOUNT></ACCOUNT>
  <RTN></RTN>
</BILLING>