al>};</span></code></pre>
<table width="90%" border="0" align="center">
  <tr> 
    <td class="table_title" colspan="8"> Iteration and filtering policies </td>
  </tr>
  <tr> 
  <tr> 
    <td class="table_cells"><b>advance</b></td>
    <td class="table_cells">Move the iterator forward</td>
  </tr>
  <td class="table_cells"><b>at_end</b></td>
    <td class="table_cells">Return true if the input is exhausted</td>
  </tr>
  <td class="table_cells"><b>filter</b></td>
    <td class="table_cells">Filter a charact