 <td headers="matches"><i>X</i>, via zero-width negative lookbehind</td></tr>

 <tr><td valign="top" headers="construct special"><tt>(?&gt;</tt><i>X</i><tt>)</tt></td>
     <td headers="matches"><i>X</i>, as an independent, non-capturing group</td></tr>

 </table>

 <hr>


 <a name="bs">
 <h4> Backslashes, escapes, and quoting </h4>

 <p> The backslash character (<tt>'\'</tt>) serves to introduce escaped
 constructs, as defined in the table above, as well as to quote characters
 that otherwise would be inte