g group</td></tr>
 <tr><td valign="top" headers="construct special"><tt>(?idmsux-idmsux)&nbsp;</tt></td>
     <td headers="matches">Nothing, but turns match flags on - off</td></tr>
 <tr><td valign="top" headers="construct special"><tt>(?idmsux-idmsux:</tt><i>X</i><tt>)</tt>&nbsp;&nbsp;</td>
     <td headers="matches"><i>X</i>, as a <a href="#cg">non-capturing group</a> with the
         given flags on - off</td></tr>

 <tr><td valign="top" headers="construct special"><tt>(?=</tt><i>X</i><tt>)</tt></td>
   