class ExternalIdBundle implements ImmutableBean, Iterable<ExternalId>,
    Serializable, Comparable<ExternalIdBundle>, ExternalBundleIdentifiable, ExternalIdOrBundle {

  public static ExternalIdBundle of(final ExternalScheme scheme, final String value) {
    return of(ExternalId.of(scheme, value));
  }

  private  ExternalIdBundle();
  private  ExternalIdBundle(final ImmutableSortedSet<ExternalId> identifiers);
  private  ExternalIdBundle(
      SortedSet<ExternalId> externalIds);

}