 </td>
</tr>
</tbody>
</table></div>
<h6>
<a name="boost_regex.syntax.basic_extended.h21"></a>
        <span class="phrase"><a name="boost_regex.syntax.basic_extended.buffer_boundaries"></a></span><a class="link" href="basic_extended.html#boost_regex.syntax.basic_extended.buffer_boundaries">Buffer
        boundaries</a>
      </h6>
<p>
        The following match only at buffer boundaries: a "buffer" in this
        context is the whole of the input text that is being matched against (note
        that ^ an