title: Knockout decorateInputElement configuration
body: <p>I can't make <em>decorateInputElement</em> working on this very basic example: <a href="http://plnkr.co/edit/A6ktDrSfcrBTURyUGNNC?p=preview" rel="nofollow">Plunker</a>.</p>
  
  <h3>HTML</h3>
  
  <pre><code>&lt;label data-bind="text: isValid()"&gt;&lt;/label&gt;
  &lt;div&gt;
    &lt;label&gt;DateTime&lt;/label&gt;
    &lt;input id="datePicker" data-bind="value: dateTime" /&gt;
    &lt;label data-bind="text: dateTime"&gt;&lt;/label&gt;
  &lt;/div&gt;
  </code></pre>
  
  <h3>JS</h3>
  
  <pre><code>$(function() {
    ko.validation.init({
      insertMessages: false,
      decorateInputElement: true
    });
  
    function ViewModel() {
      var self = this;
      self.dateTime = ko.observable().extend({
        required: true
      });
    }
  
    var viewModel = ko.validatedObservable(new ViewModel())();
    ko.applyBindings(viewModel);
  });
  </code></pre>
  
  <h3>CSS</h3>
  
  <pre><code>.validationMessage {
    color: red;
  }
  
  .validationElement {
    background: red;
  }
  </code></pre>
  
  <p>Normally, <em>validationElement</em> class should be applied when the field is empty but nothing happens (<em>insertMessages</em> works, however). Any idea?</p>