showdownjs/test/features/tables/basic_with_header_ids.html

<table>
    <thead>
    <tr>
        <th id="first_header">First Header</th>
        <th id="second_header">Second Header</th>
    </tr>
    </thead>

    <tbody>
    <tr>
        <td>Row 1 Cell 1</td>
        <td>Row 1 Cell 2</td>
    </tr>

    <tr>
        <td>Row 2 Cell 1</td>
        <td>Row 2 Cell 2</td>
    </tr>

    </tbody>
</table>