      of an expression, or the last character of a sub-expression.
      </p>
<h5>
<a name="boost_regex.syntax.basic_extended.h4"></a>
        <span class="phrase"><a name="boost_regex.syntax.basic_extended.marked_sub_expressions"></a></span><a class="link" href="basic_extended.html#boost_regex.syntax.basic_extended.marked_sub_expressions">Marked
        sub-expressions:</a>
      </h5>
<p>
        A section beginning <code class="computeroutput"><span class="special">(</span></code> and ending
        <cod