>
 <tr><td valign="top" headers="construct predef"><tt>\d</tt></td>
     <td headers="matches">A digit: <tt>[0-9]</tt></td></tr>

 <tr><td valign="top" headers="construct predef"><tt>\D</tt></td>
     <td headers="matches">A non-digit: <tt>[^0-9]</tt></td></tr>
 <tr><td valign="top" headers="construct predef"><tt>\s</tt></td>
     <td headers="matches">A whitespace character: <tt>[ \t\n\x0B\f\r]</tt></td></tr>
 <tr><td valign="top" headers="construct predef"><tt>\S</tt></td>

     <td headers="matches">A no