code: public static synchronized void registerEngine(RenderEngine engine) {
      if (null == availableEngines) {
        availableEngines = new HashMap();
      }
      availableEngines.put(engine.getName(), engine);
    }
docs: Different RenderEngines can register themselves with the
  EngineManager factory to be available with EngineManager.getInstance();
  
  @param engine RenderEngine instance, e.g. SnipRenderEngine