code: protected StringBuilder appendTo(StringBuilder builder) {
      return jobId.appendTo(builder).
                   append(SEPARATOR).
                   append(isMap ? 'm' : 'r').
                   append(SEPARATOR).
                   append(idFormat.format(id));
    }
docs: Add the unique string to the given builder.
  @param builder the builder to append to
  @return the builder that was passed in