e class="computeroutput"><span class="special">)</span></code> acts as a marked sub-expression.
        Whatever matched the sub-expression is split out in a separate field by the
        matching algorithms. Marked sub-expressions can also repeated, or referred
        to by a back-reference.
      </p>
<h5>
<a name="boost_regex.syntax.basic_extended.h5"></a>
        <span class="phrase"><a name="boost_regex.syntax.basic_extended.repeats"></a></span><a class="link" href="basic_extended.html#boost_regex.syn