code: public static String getDigitsFromHexLiteral(String paramString) {
          Matcher matcher = SingleQuotedHexLiteral.matcher(paramString);
          if (matcher.matches()) {
              return matcher.group(1);
          }
          return null;
      }
docs: Given a parameter string, if it's of the form x'0123456789ABCDEF',
  return a string containing just the digits.  Otherwise, return null.