code: @Override
      public void addSourceTargetSet(UnicodeSet inputFilter, UnicodeSet sourceSet, UnicodeSet targetSet) {
          sourceSet.addAll(getFilterAsUnicodeSet(inputFilter));
          for (EscapeTransliterator it = this; it != null ; it = it.supplementalHandler) {
              if (inputFilter.size() != 0) {
                  targetSet.addAll(it.prefix);
                  targetSet.addAll(it.suffix);
                  StringBuilder buffer = new StringBuilder();
                  for (int i = 0; i < it.radix; ++i) {
                      Utility.appendNumber(buffer, i, it.radix, it.minDigits);
                  }
                  targetSet.addAll(buffer.toString()); // TODO drop once String is changed to CharSequence in UnicodeSet
              }
          }
      }
docs: /* (non-Javadoc)
  @see android.icu.text.Transliterator#addSourceTargetSet(android.icu.text.UnicodeSet, android.icu.text.UnicodeSet, android.icu.text.UnicodeSet)