title: PHP get every third item of list
body: <p>I have used this code to toggle between classes for odd/even elements:</p>
  
  <pre><code>&lt;li class="&lt;?php echo ($key%2) ? "odd" : "even";&gt;
  </code></pre>
  
  <p>How can I get every 3rd item, to add ex. classes 'one', 'two, 'three'?</p>