Creating and managing schemas within google cloud pub/sub

[jredl]

While reviewing the google cloud pub sub schema registry: https://cloud.google.com/pubsub/docs/schemas#go

It isn't clear how google manages schema versioning or schema evolution? For example it doesn't seem possible to perform an edit on a schema? Does that mean that any additive change is always a new version? If so, how would the team recommend that we tag the version of the schema?