title: Knockout Validation Checkbox List Required Validation Message
body: <p>I am trying to create a Checkbox List using Knockout and require that at least one Checkbox is checked using Knockout Validation.</p>
  
  <p>The issue that I am having is that the required validation message appears multiple times, once for each option, if no checkbox is checked.  How do I resolve this issue?</p>
  
  <p>working example: <a href="http://jsfiddle.net/aaronhoffman/BtK3t/" rel="nofollow">http://jsfiddle.net/aaronhoffman/BtK3t/</a></p>
  
  <p>The HTML</p>
  
  <pre><code>&lt;script id="koValidationCustomMessageTemplate" type="text/html"&gt;
      &lt;em class="text-danger" data-bind="validationMessage: field"&gt;&lt;/em&gt;
  &lt;/script&gt;
  
  &lt;div class="col-sm-5" data-bind="foreach: TheCheckboxListOptions"&gt;
      &lt;div class="checkbox"&gt;
          &lt;label&gt;
              &lt;input type="checkbox" data-bind="value: $data, checked: $root.TheCheckboxListSelectedValues" /&gt;&lt;span data-bind="text: $data"&gt;&lt;/span&gt;
          &lt;/label&gt;
      &lt;/div&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>and the javascript</p>
  
  <pre><code>ko.validation.configure({
      registerExtenders: true,
      messagesOnModified: true,
      insertMessages: true,
      parseInputAttributes: true,
      messageTemplate: "koValidationCustomMessageTemplate"
  });
  
  var TheViewModel = {
  
      TheCheckboxListOptions: [
          "Option 1",
          "Option 2",
          "Option 3",
          "Option 4"
      ],
  
      TheCheckboxListSelectedValues: ko.observableArray().extend({
          required: { message: "At least one option is required." }
      }),
  
  };
  
  
  ko.applyBindings(TheViewModel);
  </code></pre>