156     unsigned long id = 0;  member
600     uint8_t id = 0;    //1: linear, 2: radial  member
724     LottieObject* content(unsigned long id)  in content()
726         if (this->id == id) return this;  in content()
732                 if (auto ret = static_cast<LottieGroup*>(child)->content(id)) return ret;  in content()
733             } else if (child->id == id) return child;  in content()
783     unsigned long rid = 0;      //pre-composition reference id.
784     int16_t mid = -1;           //id of the matte layer.
800     LottieLayer* layerById(unsigned long id)  in layerById()
805             if (layer->id == id) return layer;  in layerById()
879     LottieLayer* asset(unsigned long id)  in asset()
883             if (layer->id == id) return layer;  in asset()