title: binding classes to TextField
body: <p>I would like to automatically highlight a Ember.TextField when the value in it is invalid.</p>
  
  <p>I have something like this in my template right now that works but is ugly:</p>
  
  <pre><code>{{#if view.fieldInvalid}}
      {{view Ember.TextField valueBinding="view.fieldValue" classNames="span1p5 highlight"}}
  {{else}}
      {{view Ember.TextField valueBinding="view.fieldValue" classnames="span1p5"}}
  {{/if}}
  </code></pre>
  
  <p>Is there a way to do this in Ember.JS with a built-in view like Ember.TextField?</p>