Get a reference to a collection.

        For a top-level collection:

        .. code-block:: python

            >>> client.collection('top')

        For a sub-collection:

        .. code-block:: python

            >>> client.collection('mydocs/doc/subcol')
            >>> # is the same as
            >>> client.collection('mydocs', 'doc', 'subcol')

        Sub-collections can be nested deeper in a similar fashion.

        Args:
            collection_path (Tuple[str, ...]): Can either be

                * A single ``/``-delimited path to a collection
                * A tuple of collection path segments

        Returns:
            ~.firestore_v1beta1.collection.CollectionReference: A reference
            to a collection in the Firestore database.

def collection(self, *collection_path):
        """Get a reference to a collection.

        For a top-level collection:

        .. code-block:: python

            >>> client.collection('top')

        For a sub-collection:

        .. code-block:: python

            >>> client.collection('mydocs/doc/subcol')
            >>> # is the same as
            >>> client.collection('mydocs', 'doc', 'subcol')

        Sub-collections can be nested deeper in a similar fashion.

        Args:
            collection_path (Tuple[str, ...]): Can either be

                * A single ``/``-delimited path to a collection
                * A tuple of collection path segments

        Returns:
            ~.firestore_v1beta1.collection.CollectionReference: A reference
            to a collection in the Firestore database.
        """
        if len(collection_path) == 1:
            path = collection_path[0].split(_helpers.DOCUMENT_PATH_DELIMITER)
        else:
            path = collection_path

        return CollectionReference(*path, client=self)