$re = '~(<tr.*?<th>.*<th>.*?</tr>)~is';
$str = '<table>
<tr>
<th>header1</th>
<th>header2</th>
<th>header3</th>
</tr>
<tr>
<th>header21</th>
<th>header22</th>
<th>header23</th>
</tr>
<tr>
<td>body1</td>
<td>body2</td>
<td>body3</td>
</tr>
<tr>
<td>body21</td>
<td>body22</td>
<td>body23</td>
</tr>
</table>';
preg_match_all($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