def _load_collections(self, attrs, resource_model, service_context):
        """
        Load resource collections from the model. Each collection becomes
        a :py:class:`~boto3.resources.collection.CollectionManager` instance
        on the resource instance, which allows you to iterate and filter
        through the collection's items.
        """
        for collection_model in resource_model.collections:
            attrs[collection_model.name] = self._create_collection(
                resource_name=resource_model.name,
                collection_model=collection_model,
                service_context=service_context,
            )

        Load resource collections from the model. Each collection becomes
        a :py:class:`~boto3.resources.collection.CollectionManager` instance
        on the resource instance, which allows you to iterate and filter
        through the collection's items.
        
boto3/resources/factory.py