code: @Override
      public String toPattern(boolean escapeUnprintable) {
          if (pat != null && !escapeUnprintable) {
              return pat;
          }
          StringBuilder result = new StringBuilder();
          return _toPattern(result, escapeUnprintable).toString();
      }
docs: Returns a string representation of this set.  If the result of
  calling this function is passed to a UnicodeSet constructor, it
  will produce another set that is equal to this one.