@Nullable
    @Override
    public ViewerAnnotator createAnnotator(@NotNull ThreesideTextDiffViewerEx viewer, @NotNull ThreeSide side) {
      if (side == ThreeSide.BASE) return null; // middle content is local Document, not the BASE one
      return super.createAnnotator(viewer, side);
    }
@Nullable
    @Override
    public ViewerAnnotator createAnnotator(@NotNull ThreesideTextDiffViewerEx viewer, @NotNull ThreeSide side)