code: public static void registerFactory(String ID, Factory factory) {
          registry.put(ID, factory, true);
      }
docs: Register a factory object with the given ID.  The factory
  method should return a new instance of the given transliterator.
  
  <p>Because ICU may choose to cache Transliterator objects internally, this must
  be called at application startup, prior to any calls to
  Transliterator.getInstance to avoid undefined behavior.
  
  @param ID the ID of this transliterator
  @param factory the factory object