code: func ValidateReservedNamespaceLabels(labels []string) error {
  	for _, label := range labels {
  		lowered := strings.ToLower(label)
  		if strings.HasPrefix(lowered, "com.docker.") || strings.HasPrefix(lowered, "io.docker.") ||
  			strings.HasPrefix(lowered, "org.dockerproject.") {
  			return fmt.Errorf(
  				"label %s not allowed: the namespaces com.docker.*, io.docker.*, and org.dockerproject.* are reserved for Docker's internal use",
  				label)
  		}
  	}
  	return nil
  }
docs: // ValidateReservedNamespaceLabels errors if the reserved namespaces com.docker.*,
  // io.docker.*, org.dockerproject.* are used in a configured engine label.
  //
  // TODO: This is a separate function because we need to warn users first of the
  // deprecation.  When we return an error, this logic can be added to Validate
  // or GetConflictFreeLabels instead of being here.