pan><span class=special>;
    </span><span class=special>...
    </span><span class=identifier>rule </span><span class=special>= </span><span class=identifier>a </span><span class=special>| </span><span class=identifier>b</span><span class=special>;</span></font></code></pre>
<p>These limitations lead us to this implementation of rules. This comes at the 
  expense of the overhead of a virtual function call, once through each invocation 
  of a rule.</p>
<p><img src="theme/lens.gif" width="15" height="16"> 