code: def bind_collection_to_model_cls(cls):
          
          cls.Collection = type('{0}.Collection'.format(cls.__name__),
                                (cls.Collection,),
                                {'value_type': cls})
          cls.Collection.__module__ = cls.__module__
docs: Bind collection to model's class.
  
          If collection was not specialized in process of model's declaration,
          subclass of collection will be created.