title: Why does the following result in "Must set Ember.set() to access this property"?
body: <p>I'm attempting to filter the content of my documents controller according to the content of my selected tags controller. I'm not sure if this is the best solution so feel free to suggest an alternative.</p>
  
  <p>Aside from that uncertainty, can anyone explain why the following results in <code>assertion failed: Must use Ember.set() to access this property</code>? Particularly <code>selectedTagsBinding: "App.selectedTagsController.content"</code> is what fails.</p>
  
  <pre><code>App = Ember.Application.create();
  
  App.documentsController = Ember.ArrayProxy.create({
      content: [],
  
      selectedTagsBinding: "App.selectedTagsController.content" 
  });
  
  App.selectedTagsController = Ember.ArrayProxy.create({
      content: [ new Ember.Object(), new Ember.Object() ]
  });
  </code></pre>