I can easily break this code by feeding it:

my $str = '<p>something something</p>
<h2>blah </a> blah blah</h2>
<p>something something</p>';
[download]

Output:

<p>something something<p>
<h1>blah <a> blah blah<h1>
<p>something something<p>
[download]

(Whered the slash before the a go? Heck if I know)