title: assigning "active" class to navigation--wordpress
body: <p>I need to assign an "active" class to my main-level navigation rendered by wordpress.</p>
  
  <p>Here's my HTML:</p>
  
  <pre><code>    &lt;li&gt;&lt;a href="/"&gt;Home&lt;/a&gt;&lt;/li&gt;
      &lt;?php wp_list_pages('title_li=&amp;exclude=21'); ?&gt;
  </code></pre>