A data cell must be associated with header cells that live in different parts of a complex table (one in a column group header, one in a row group header). Which mechanism reliably links it, and how must the referenced ids be unique?
<th id="region" scope="colgroup">Region</th>
<th id="q1" scope="rowgroup">Q1</th>
<td headers="region q1">$5,000</td>