Beefed up the comments for AppConfig.all_models.

            return cls(entry)

    def import_models(self, all_models):

        # Dictionary of models for this app, stored in the 'all_models'

        # attribute of the Apps this AppConfig is attached to. Injected as a

        # parameter because it may get populated before this method has run.

        # Dictionary of models for this app, primarily maintained in the

        # 'all_models' attribute of the Apps this AppConfig is attached to.

        # Injected as a parameter because it gets populated when models are

        # imported, which may happen before populate_models() runs.

        self.models = all_models

        if module_has_submodule(self.app_module, MODELS_MODULE_NAME):

        # get_model[s].

        self.master = master

        # Mapping of app labels => model names => model classes. Used to

        # register models before the registry is populated and also for

        # applications that aren't installed.

        # Mapping of app labels => model names => model classes. Every time a

        # model is imported, ModelBase.__new__ calls apps.register_model which

        # creates an entry in all_models. All imported models are registered,

        # regardless of whether they're defined in an installed application

        # and whether the registry has been populated. Since it isn't possible

        # to reimport a module safely (it could reexecute initialization code)

        # all_models is never overridden or reset.

        self.all_models = defaultdict(OrderedDict)

        # Mapping of labels to AppConfig instances for installed apps.