onblur question

Code:

<script type="text/javascript">
   window.onload = function()
   {
      CKEDITOR.replace( 'editor1' );
      CKEDITOR.instances.editor1.on('OnBlur', function() {
         alert('onblur fired');
      });
      alert( CKEDITOR.version );
   };
</script>

I'm not sure I'm using this correctly although the second alert (the code version) does work.

There are no errors in loading the page.

When moving focus away from the editor1 CK Editor object, the onblur event does not respond.

Thanks