!/usr/bin/perl

use strict;
use warnings;

use XML::LibXML;

my $xml = <<'XML';
<FILER url='http://somewhere'>
<PROJECT name='test_project'/>
<USER email='some@email.com'/>
</FILER>
XML

my $parser = XML::LibXML->new();
my $doc    = $parser->parse_string( $xml );

my $node   = $doc->createElement( 'LOCATION' );
   $node->setAttribute( 'name', '1stFloor' );

my $root   = $doc->documentElement();
   $root->appendChild( $node );

print $doc->toString(), "\n";