    <td><p>used as label if label_key does not exist in given
<code>tf$Example</code>. By default default_value is none, which means
<code>tf$parse_example</code> will error out if there is any missing label.</p></td>
    </tr>
    <tr>
      <th>label_dimension</th>
      <td><p>Number of regression targets per example. This is the
size of the last dimension of the labels and logits <code>Tensor</code> objects
(typically, these have shape <code>[batch_size, label_dimension]</code>).</p></td>
    </tr>
    