special>)
    </span><span class=special>)</span></code></pre>
<p>Subrule IDs need to be unique only within a group. A grammar is an implicit 
  group. Furthermore, even subrules in a grammar may have the same IDs without 
  clashing if they are inside a group. Subrules may be explicitly grouped using 
  the parentheses. Parenthesized groups have unique scopes. In the code above, 
  the outer subrule group defines the subrules <tt>a</tt> and <tt>b</tt> while 
  the inner subrule group defines the subrules <