To make sure that API clients do not overwrite each other's data, this API supports optimistic concurrency control for PUT operations by including an Etag header. When the client updates a resource, it can include an optional If-Match header with the ETag header value it received from the GET. When the client provides an If-Match header, the request succeeds if the state matches what the client is updating as indicated by the ETag; otherwise it issues a 412 error.