Example
A cell containing header information for a row in a grid.
<table role="grid">
<thead>
<!-- etc -->
</thead>
<tbody>
<tr>
<th role="rowheader">Day 1</th>
<td>65</td>
</tr>
<tr>
<th role="rowheader">Day 2</th>
<td>74</td>
</tr>
</tbody>
</table>