$re = '/(<tr class="class1">)([\s\S]*?)(<\/tr>)/m';
$str = '<tr class="class1">
<td class="class2">
<a href="some_address"></a>
<div id="id1">
<span class="class3"></span>
</div>
<span>Just a text</span>
</td>
</tr>';
preg_match_all($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