Stop. This folder is likely not what you are looking for.
This folder contains protocol buffer definitions for test-only API for Cloud Spanner clients. Unless told otherwise by a Google Cloud representative, do not use any of the contents of this folder. If you would like to use Cloud Spanner, please consult our official documentation for details on our APIs, or else consider one of our client libraries.
This API defined in this folder is unreleased and may shut off, break, or fail at any time for any users who are not registered as a part of a private preview program.