code: public static RubyRange<String> range(String start, String end) {
      return new RubyRange<>(StringSuccessor.getInstance(), start, end,
          Interval.CLOSED);
    }
docs: Creates a {@link RubyRange} by given strings.
  
  @param start
  of the range
  @param end
  of the range
  @return {@link RubyRange}