code: public static boolean isKnownCountryCode(String aCountryCode) {
          if (aCountryCode == null || aCountryCode.length() != 2) {
              return false;
          }
          return indexOf(aCountryCode) >= 0;
      }
docs: Returns whether the given string is a known country code.
  @param aCountryCode the string to evaluate.
  @return {@code true} if {@code aCountryCode} is a two-letter, uppercase String present in {@link #getKnownCountryCodes()}.