docs: function _immediateObserver() {
      _emberMetalDebug.deprecate('Usage of `Ember.immediateObserver` is deprecated, use `Ember.observer` instead.', false, { id: 'ember-metal.immediate-observer', until: '3.0.0' });
  
      for (var i = 0, l = arguments.length; i < l; i++) {
        var arg = arguments[i];
        _emberMetalDebug.assert('Immediate observers must observe internal properties only, not properties on other objects.', typeof arg !== 'string' || arg.indexOf('.') === -1);
      }
  
      return observer.apply(this, arguments);
    }