For playing with HTML, I prefer enforcing XHTML and playing with that, instead. Using XML::Twig. For example: 

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

my $html_code = '
<html>
 <head>
 <title>Glossary</title>
 </head><body> <!-- had to close head, open body -->
 <h1>Glossary</h1>
<dl>
<dt><b>E Definition</b></dt>
<dd>E - data</dd>
<p></p>
<dt><b>B Definition</b></dt>
<dd>B - data</dd>
<p></p>
<dt><b>A_definition</b></dt>
<dd>A data.</dd>
<p></p>
<dt><b>C definition</b></dt>
<dd>C - data</dd>
<p></p>
</dl>
 </body>
 </html>
';

my $twig = XML::Twig->new(pretty_print => 'indented');
$twig->parse($html_code);

for my $dl ($twig->root()->get_xpath('//dl'))
{
    my @entries;
    for my $el ($dl->children())
    {
        $el->cut();
        if ($el->gi() eq 'dt')
        {
            push @entries, [ $el ];
        }
        else
        {
            push @{$entries[-1]}, $el;
        }
    }
    @entries = sort {
        $a->[0]->text() cmp $b->[0]->text()
    } @entries;
    for my $entry (@entries)
    {
        $_->paste(last_child => $dl) for @$entry;
    }

    print $dl->sprint(),"\n";
}

[download]
Tested. The only caveat is if you start getting funky characters that aren't part of standard XML, e.g., "&copy;". Then it's a bit more work. Still doable, but more work.

In reply to Re: HTML::TreeBuilder: sort a Definition List (<dl>) by Tanktalus
in thread HTML::TreeBuilder: sort a Definition List (<dl>) by svenXY

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
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