docs: def in6_isincluded(addr, prefix, plen):
      """
      Returns True when 'addr' belongs to prefix/plen. False otherwise.
      """
      temp = inet_pton(socket.AF_INET6, addr)
      pref = in6_cidr2mask(plen)
      zero = inet_pton(socket.AF_INET6, prefix)
      return zero == in6_and(temp, pref)