 headers="matches"><tt>a</tt> through <tt>d</tt>,
      or <tt>m</tt> through <tt>p</tt>: <tt>[a-dm-p]</tt> (union)</td></tr>

 <tr><td valign="top" headers="construct classes"><tt>[a-z&&[def]]</tt></td>
     <td headers="matches"><tt>d</tt>, <tt>e</tt>, or <tt>f</tt> (intersection)</tr>
 <tr><td valign="top" headers="construct classes"><tt>[a-z&&[^bc]]</tt></td>

     <td headers="matches"><tt>a</tt> through <tt>z</tt>,
         except for <tt>b</tt> and <tt>c</tt>: <tt>[ad-z]</tt> (subtraction)</td></tr>
