title: Is it possible to select every other group of three in CSS?
body: <p>Is it possible to select every other group of three in CSS? And if it is; how?</p>
  
  <p>So in the sample below apply style to the 4-6 and 10-12 <code>li</code>s.</p>
  
  <pre><code>&lt;ul&gt;
      &lt;li&gt;1&lt;/li&gt;
      &lt;li&gt;2&lt;/li&gt;
      &lt;li&gt;3&lt;/li&gt;
       &lt;li&gt;4&lt;/li&gt;
       &lt;li&gt;5&lt;/li&gt;
       &lt;li&gt;6&lt;/li&gt;
      &lt;li&gt;7&lt;/li&gt;
      &lt;li&gt;8&lt;/li&gt;
      &lt;li&gt;9&lt;/li&gt;
       &lt;li&gt;10&lt;/li&gt;
       &lt;li&gt;11&lt;/li&gt;
       &lt;li&gt;12&lt;/li&gt;
  &lt;/ul&gt;
  </code></pre>
  
  <p>I know [pure] JavaScript and jQuery can do this but I am looking for a pure CSS solution if it exists.</p>