s declaration shall match itself: in
            other words the escape character is not "special" inside a
            character class declaration; so <code class="computeroutput"><span class="special">[\^]</span></code>
            will match either a literal '\' or a '^'.
          </li>
</ul></div>
<p>
        However, that's rather restrictive, so the following standard-compatible
        extensions are also supported by Boost.Regex:
      </p>
<h6>
<a name="boost_regex.syntax.basic_extended.h17"></a>
