title: Add class to select2 element
body: <p>The documentation is either terrible or I'm missing something.  I'm trying to add an error class to a select2 box for form validation. It's just a 1px red border.</p>
  
  <p>I found the <code>containerCssClass</code> method in the documentation, but I'm not sure how to apply it.</p>
  
  <p>I have tried the following with no luck:</p>
  
  <pre><code>$("#myBox").select2().containerCssClass('error');
  </code></pre>