an class="term">Returns:</span></p></td>
<td>the <code class="computeroutput">typeid</code> of the
              contained value if instance is non-empty, otherwise
              <code class="computeroutput">typeid(void)</code>.</td>
</tr>
<tr>
<td><p><span class="term">Notes:</span></p></td>
<td>Useful for querying against types known
              either at compile time or only at
              runtime.</td>
</tr>
</tbody>
</table></div>
</li>
</ol></div>
</div>
</div>
</div>
<table xmlns:rev="http://www.