       </p>
                  </td>
<td>
                    <p>
                      If <code class="computeroutput"><span class="identifier">f</span></code> evaluates
                      to <code class="computeroutput"><span class="keyword">true</span></code>, return
                      a zero length match.
                    </p>
                  </td>
</tr>
</tbody>
</table></div>
<h6>
<a name="spirit.qi.reference.auxiliary.eps.h7"></a>
            <span class="phrase"><a name="spirit.qi.referenc