code: public static String getRegion(String id) {
          String region = null;
          // "Etc/Unknown" is not a system time zone ID,
          // but in the zone data.
          if (!id.equals(UNKNOWN_ZONE_ID)) {
              region = ZoneMeta.getRegion(id);
          }
          if (region == null) {
              // unknown id
              throw new IllegalArgumentException("Unknown system zone id: " + id);
          }
          return region;
      }
docs: <strong>[icu]</strong> Returns the region code associated with the given
  system time zone ID. The region code is either ISO 3166
  2-letter country code or UN M.49 3-digit area code.
  When the time zone is not associated with a specific location,
  for example - "Etc/UTC", "EST5EDT", then this method returns
  "001" (UN M.49 area code for World).
  @param id the system time zone ID.
  @return the region code associated with the given
  system time zone ID.
  @throws IllegalArgumentException if <code>id</code> is not a known system ID.
  @see #getAvailableIDs(String)