      The overloads that accept a string, return the string that matched the named
        sub-expression <span class="emphasis"><em>n</em></span>. In the event that there is no such
        named sub-expression then returns an empty string.
      </p>
<p>
        The template overloads of this function, allow the string and/or character
        type to be different from the character type of the underlying sequence and/or
        regular expression: in this case the characters will be widened to the underl