I can't make a lot of sense of the documentation either. However the following code may help:

use warnings;
use strict;
use XML::Twig;

my $filtername = 'Advanced Perl Programming';
my $books_tree= new XML::Twig(twig_roots => {Title => \&FixName});

$books_tree->parse(join "", <DATA>);
#$books_tree->set_att(Name => 'Advanced Perl');

sub FixName
{
my ($p1, $p2) = @_;
my %node = %$p2;
print $node{"att"}{"Name"}."\n";
}
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