* www.google.com} is {@code google.com}.
   *
   * @throws IllegalStateException if the domain has no parent, as determined by {@link #hasParent}
   */
  public InternetDomainName parent() {
    checkState(hasParent(), "Domain '%s' has no parent", name);
    return ancestor(1);
  }

  /**
   * Returns the ancestor of the current domain at the given number of levels "higher" (rightward)