 S3 class <code>returns</code>, each
element of which is treated as a security.</p></td>
    </tr>
    <tr>
      <th>event_start</th>
      <td><p>an object of <code>Date</code> class giving the first date of
the event period.</p></td>
    </tr>
    <tr>
      <th>event_end</th>
      <td><p>an object of <code>Date</code> class giving the last date of the
event period.</p></td>
    </tr>
    </table>

    <h2 class="hasAnchor" id="value"><a class="anchor" href="#value"></a>Value</h2>

    <p>A data frame o