Sub level observator

HTML

<script src="https://raw.github.com/emberjs/starter-kit/master/js/libs/handlebars-1.0.0.beta.6.js"></script>
<script src="http://cloud.github.com/downloads/emberjs/ember.js/ember-1.0.pre.js"></script>
<script type="text/x-handlebars">
</script>

JavaScript

App = Ember.Application.create({ });


App.Day = Ember.ArrayProxy.extend({
    name: '',
    init: function() {
        this._super();
        this.set('content', []);
    }
});

App.Event = Ember.Object.extend({
    title: '',
    day: null
});

App.day_list = Ember.A();

Ember.addObserver(
   App.day_list,
   '[]',
    function() {
        console.log('foobar');
    }
);

monday = App.Day.create({ name: 'Monday' }); 
App.day_list.pushObject(monday); // Show foobar here => good
console.log('---');
monday.pushObject(App.Event.create({ title: 'event 1' })); // Don't show foobar here => fail :(