ric</code> or <code>integer</code>.</p></td>
    </tr>
    <tr>
      <th>header_cells</th>
      <td><p>Data frame of header cells with at least the columns
'row' and 'column', which are numeric/integer vectors.</p></td>
    </tr>
    <tr>
      <th>direction</th>
      <td><p>The direction between a data cell and its header, one of
<code>"up"</code>, <code>"right"</code>, <code>"down"</code>, <code>"left"</code>, <code>"up-left"</code>, <code>"up-right"</code>,
<code>"right-up"</code>, <code>"right-down"<