title: signaling an error in FreeMarker
body: <p>Scenario:</p>
  
  <ul>
  <li>I have a Java program that is fixed, that uses FreeMarker templates</li>
  <li>I am the one writing the FreeMarker templates.</li>
  <li>In one of my templates, I want to check a value, and if it is out of bounds, signal an error back up to the application.</li>
  </ul>
  
  <p>How can I do this? There is the <a href="http://freemarker.org/docs/ref_directive_attempt.html" rel="nofollow"><code>attempt/recover</code></a> mechanism analogous to <code>try/catch</code>, but there's no equivalent to <code>throw</code>. (other than the <code>stop</code> directive)</p>