code: func validateSettings(ctx *validation.Context, settings *notifypb.Settings) {
  	switch {
  	case settings.MiloHost == "":
  		ctx.Errorf(requiredFieldError, "milo_host")
  	case validation.ValidateHostname(settings.MiloHost) != nil:
  		ctx.Errorf(invalidFieldError, "milo_host")
  	}
  }
docs: // validateSettings returns an error if the service configuration violates any
  // of the requirements in the proto definition.