I would definitely use XML::LibXML or XML::XSH2. But they work differently to XML::Twig or XML::Simple. It's best to work directly on the DOM object instead of creating a structure that you need to serialize back to XML later.

It's a bit garrulous, but something like this creates the same structure from the ;xmlstyle=flat:

#! /usr/bin/perl
use strict;
use warnings;
use Data::Dump qw{ pp };

use XML::LibXML;

sub with_id {
    my ($dom, $xpath) = @_;
    return { name => $dom->findvalue("normalize-space($xpath)"),
             id   => $dom->findvalue("$xpath/\@id"), }
}

my $dom = 'XML::LibXML'->load_xml(IO => *DATA);

my %node = (
    author    => with_id($dom, '/node/author'),
    type      => with_id($dom, '/node/type'),
);

@node{qw{ created updated title }}
    = @{ $dom->findnodes('/node')->[0] }{qw{ created updated title }};

@node{qw{ content parent root reputation }}
    = map $dom->findvalue("/node/$_"),
          qw( doctext parent_node root_node reputation );

print pp \%node;

__DATA__
...
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