xpath -e '//*[not(child::*)]' books.xml

##</code><code>##

use strict;
use warnings;

use XML::XPath;
use XML::XPath::XMLParser;
    
my $xp = XML::XPath->new(filename => 'books.xml');
    
my $nodeset = $xp->find('//*[not(child::*)]');
    
foreach my $node ($nodeset->get_nodelist) {
    print "FOUND:", 
        XML::XPath::XMLParser::as_string($node),
        "\n";
}