ss="identifier">fp</span></code> will be
                      invoked at parse time. <code class="computeroutput"><span class="identifier">fp</span></code>
                      is expected to return a <a class="link" href="../parser_concepts/parser.html" title="Parser"><code class="computeroutput"><span class="identifier">Parser</span></code></a> object. This
                      parser is then invoked in order to parse the input.
                    </p>
                  </td>
</tr>
</tbody>
</table></