$doc = new DOMDocument();
$doc->loadhtml('<table>
<tr>
<th>table header</th>
<td>table cell</td>
</tr>
</table>');

$xpath = new DOMXPath($doc);

$rows = $xpath->query('//tr');                        // select all <tr> elements anywhere in the document
$cols = $xpath->query('./th | ./td',$rows->ITem(0)); // select all <th>/<td> From context
                                                      // where context = First row
echo $cols->length;             // 2
echo $cols->item(0)->nodeValue; // table header
echo $cols->item(1)->nodeValue; // table cell