code: @Override public Frames fillImpl(Frames f) {
      super.fillImpl(f);
  
      if (frames != null) {
        f.frames = new Frame[frames.length];
  
        int i = 0;
        for (FrameBaseV3 frame : this.frames) {
          f.frames[i++] = frame._fr;
        }
      }
      return f;
    }
docs: Non-version-specific filling into the impl