code: @Override
      public void addReplacementSetTo(UnicodeSet toUnionTo) {
          int ch;
          for (int i=0; i<output.length(); i+=UTF16.getCharCount(ch)) {
              ch = UTF16.charAt(output, i);
              UnicodeReplacer r = data.lookupReplacer(ch);
              if (r == null) {
                  toUnionTo.add(ch);
              } else {
                  r.addReplacementSetTo(toUnionTo);
              }
          }
      }
docs: Union the set of all characters that may output by this object
  into the given set.
  @param toUnionTo the set into which to union the output characters