$re = '/<div[^>]*>((?:(?R)|(?:(?!<\/?div)[\s\S]))*)<\/div>/m';
$str = '<div class="1">abc
<!--
comentario </div>
-->
xyz
</div>
<div class="1" >
abc
<p>div2</p>
xyz
</div>';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php