title: Less CSS :extend() doesn't work when an extra selector is attached to parent selector
body: <p>I was wondering why does this work</p>
  
  <pre><code>&amp;:extend(.test all);
  </code></pre>
  
  <p>but</p>
  
  <pre><code>&amp;.a_class:extend(.test all);
  </code></pre>
  
  <p>doesn't work?</p>