title: Using Knockout to check if undefined
body: <p>I have a template that I would like to use a different bit of HTML based on the control being used:</p>
  
  <pre><code>&lt;!-- ko if: Value --&gt;
      ........
  &lt;!-- /ko --&gt;
  
  &lt;!-- ko ifnot: Value --&gt;
      ........
  &lt;!-- /ko --&gt;
  </code></pre>
  
  <p>The intention of this code is to select the first bit if <code>Value</code> is defined, the second bit if not. However, this always causes a binding error: <code>Value is not defined</code> which I'm fairly sure errors out just checking if the control has <code>Value</code> defined. </p>
  
  <p>Is there a better way to use these if statements to check if a binding is defined or not?</p>