android/guava/src/com/google/common/net/InternetDomainName.java
private InternetDomainName ancestor(int levels) {
    return from(DOT_JOINER.join(parts.subList(levels, parts.size())));
  }
private InternetDomainName ancestor(int levels) {
    return from(DOT_JOINER.join(parts.subList(levels, parts.size())));
  }
Returns the ancestor of the current domain at the given number of levels "higher" (rightward)
in the subdomain list. The number of levels must be non-negative, and less than {@code N-1},
where {@code N} is the number of parts in the domain.

<p>TODO: Reasonable candidate for addition to public API.