title: How do I validate a non-model form in Rails 3?
body: <p>Let's say I have a search form and I want to validate the length of the keyword. I want the form to highlight the invalid field (like model forms). I've looked everywhere and can't seem to find any useful information on validating non-model-backed forms in Rails 3. I've tried the <em>validatable</em> gem, but this doesn't seem to work with Rails 3:</p>
  
  <pre><code>undefined method `model_name' for Login:Class.
  </code></pre>
  
  <p>Any ideas?</p>