code: public static Parser<Void> among(String chars) {
      if (chars.length() == 0) return isChar(CharPredicates.NEVER);
      if (chars.length() == 1) return isChar(chars.charAt(0));
      return isChar(CharPredicates.among(chars));
    }
docs: A scanner that succeeds and consumes the current character if it equals to any character in
  {@code chars}.