title: Symfony - Add class to form tag
body: <p>I know I can add classes to <code>&lt;input&gt;</code> fields in a form like this:</p>
  
  <pre><code>-&gt;add('foo', 'text', array('attr' =&gt; array('class' =&gt; 'foo-class'));
  </code></pre>
  
  <p>but how could I add a class to a <code>&lt;form&gt;</code> tag?</p>