<update nr="4"> For the sake of completeness, here's a working script with the changes mentioned below:

use warnings;
use strict;
use XML::LibXML;

my $doc = XML::LibXML->load_xml( location => 'example.xhtml',
    no_network=>1, recover=>1 );
my $xpc = XML::LibXML::XPathContext->new($doc);
$xpc->registerNs('html', 'http://www.w3.org/1999/xhtml');
my @ids2text = map { [ $_->getAttribute('id'), $_->textContent ] }
    $xpc->findnodes(q{//html:div[@class='data']});

$_->[1] =~ s/\W+//g for @ids2text;

print join ", ", map sprintf("%s=%s", @$_), @ids2text;
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</update>

Thanks very much for the reply! Your post inspired some more test cases for my file, and I'm sorry to say I broke your code :-( But here's the fix:

my @ids2text = map { [ $_->getAttribute('id'), $_->textContent ] }
    $doc->findnodes(q{//div[@class='data']});
[download]

Update: And yes, it does seem that load_html doesn't like XHTML - load_xml seems to work a bit better, although fetching the DTD from the net is pretty slow at the moment; adding the options {no_network=>1,recover=>1} disables the network check. However, with load_xml one also has to start using XML::LibXML::XPathContext:

my $xpc = XML::LibXML::XPathContext->new($doc);
$xpc->registerNs('html', 'http://www.w3.org/1999/xhtml');
my @ids2text = map { [ $_->getAttribute('id'), $_->textContent ] }
    $xpc->findnodes(q{//html:div[@class='data']});
[download]

Update 2: Even with network, XML::LibXML is still complaining about &nbsp; ("Entity 'nbsp' not defined"), I'm not entirely sure why yet, as it seems to be defined in the DTD... Update 3: The W3C Validator doesn't complain...