def collections(self, page_size=None):
        """List subcollections of the current document.

        Args:
            page_size (Optional[int]]): The maximum number of collections
            in each page of results from this request. Non-positive values
            are ignored. Defaults to a sensible value set by the API.

        Returns:
            Sequence[~.firestore_v1beta1.collection.CollectionReference]:
                iterator of subcollections of the current document. If the
                document does not exist at the time of `snapshot`, the
                iterator will be empty
        """
        iterator = self._client._firestore_api.list_collection_ids(
            self._document_path,
            page_size=page_size,
            metadata=self._client._rpc_metadata,
        )
        iterator.document = self
        iterator.item_to_value = _item_to_collection_ref
        return iterator
List subcollections of the current document.

        Args:
            page_size (Optional[int]]): The maximum number of collections
            in each page of results from this request. Non-positive values
            are ignored. Defaults to a sensible value set by the API.

        Returns:
            Sequence[~.firestore_v1beta1.collection.CollectionReference]:
                iterator of subcollections of the current document. If the
                document does not exist at the time of `snapshot`, the
                iterator will be empty