title: Zend Form: add error message after form validation
body: <p>How to add an error message to Zend Form element after the form was already validated?</p>
  
  <p>I'm trying to add error mesages I get from <code>Zend_Auth</code> (now I'm displaying them using flashMessenger).</p>
  
  <p>I tried something like this:</p>
  
  <pre><code>$form-&gt;getElement('username')-&gt;addErrorMessage('my message');
  </code></pre>