up alternations, for example: <code class="computeroutput"><span class="identifier">ab</span><span class="special">(</span><span class="identifier">d</span><span class="special">|</span><span class="identifier">ef</span><span class="special">)</span></code>
        will match either of "abd" or "abef".
      </p>
<h5>
<a name="boost_regex.syntax.basic_extended.h8"></a>
        <span class="phrase"><a name="boost_regex.syntax.basic_extended.character_sets"></a></span><a class="link" href="basic_extended.html