code: public static Set<String> getAvailableIDs(SystemTimeZoneType zoneType,
              String region, Integer rawOffset) {
          return ZoneMeta.getAvailableIDs(zoneType, region, rawOffset);
      }
docs: <strong>[icu]</strong> Returns a set of time zone ID strings with the given filter conditions.
  <p><b>Note:</b>A <code>Set</code> returned by this method is
  immutable.
  @param zoneType      The system time zone type.
  @param region        The ISO 3166 two-letter country code or UN M.49 three-digit area code.
  When null, no filtering done by region.
  @param rawOffset     An offset from GMT in milliseconds, ignoring the effect of daylight savings
  time, if any. When null, no filtering done by zone offset.
  @return an immutable set of system time zone IDs.
  @see SystemTimeZoneType