$re = '/(<)(br|div)([^>]+?)(\/?\s*>)/mi';
$str = '<br id="foo" style="display:none">
<spam id="bar">sometext</span>
<br id="bun" />
<div class="foo">
<div class="bar">
<a href="baz.php">baz</a>
</div>
</div>';
$subst = "\1\2\4";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
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