title: knockout.validation.js error in IE8, observable does not support 'extend' property or method
body: <p>Our knockout validation setup works on FF, Chrome, IE 10 and 9. In IE8 we get the error: </p>
  
  <p>SCRIPT438: Object doesn't support property or method 'extend' 
  knockout.validation.js, line 353 character 17</p>
  
  <p>This is when knockout is trying to add a rule, the observable being passed is a boolean value not a function as it should be. Not sure why a boolean is being passed. We have quite a few constructs like this for e.g.:
  self.MiddleInitial = ko.observable().extend({ maxLength: 1 });</p>
  
  <p>if we comment out all of the knockout-extends, then we have no error</p>
  
  <p>related html looks like this:</p>
  
  <p></p>
  
  <p>Site is ASP.Net/MVC. versions: knockout 2.2.1.debug, modernizr-2.6.2, jquery 1.10.1, jquery-ui-1.10.3    </p>
  
  <p>Thanks in advance.          </p>
  
  <p>It seems the error happens when knockout tries to add a "requires" rule on a set of checkboxes. The related observable does not have any validation specified for it.</p>