title: checkbox non boolean value?
body: <p>I have the following example:
  <a href="http://jsfiddle.net/jLkxG/6/" rel="nofollow">http://jsfiddle.net/jLkxG/6/</a></p>
  
  <p>The is_checked property can have 2 values: Yes or No. The checkbox should be checked if the value is yes and when the saved link is clicked, the property should be assigned yes or no depending on whether checkbox is checked.</p>
  
  <p>How would you do this in knockoutjs?</p>