th>
     <td><tt>((A)(B(C)))</tt></td></tr>
 <tr><th>2&nbsp;&nbsp;&nbsp;&nbsp;</th>
     <td><tt>(A)</tt></td></tr>
 <tr><th>3&nbsp;&nbsp;&nbsp;&nbsp;</th>
     <td><tt>(B(C))</tt></td></tr>

 <tr><th>4&nbsp;&nbsp;&nbsp;&nbsp;</th>
     <td><tt>(C)</tt></td></tr>
 </table></blockquote>

 <p> Group zero always stands for the entire expression.

 <p> Capturing groups are so named because, during a match, each subsequence
 of the input sequence that matches such a group is saved.  The captured
 subsequence may