title: ko.computed write function on foreach $data variable
body: <p>is it possible use the ko.computed write function on the foreach $data variable like this?</p>
  
  <pre><code>&lt;!-- ko foreach: activeAttributes.optionsSplitted --&gt;
      &lt;input type="text" data-bind="value: $data"&gt;
  &lt;!-- /ko --&gt;
  
  
  vm.activeAttributes.optionsSplitted = ko.computed({
      read: function(){
          return vm.activeAttributes().options().split("-*!*-");      
      },
      write: function(){
          alert("changed");
      }
  });
  </code></pre>