code: @SuppressWarnings("unused")
      public final void addItemDecoration(RecyclerView.ItemDecoration decor, int index) {
          getRvCategories().addItemDecoration(decor, index);
      }
docs: Add an {@link RecyclerView.ItemDecoration} to wrapped RecyclerView. Item decorations can
  affect both measurement and drawing of individual item views.
  <p>
  <p>Item decorations are ordered. Decorations placed earlier in the list will
  be run/queried/drawn first for their effects on item views. Padding added to views
  will be nested; a padding added by an earlier decoration will mean further
  item decorations in the list will be asked to draw/pad within the previous decoration's
  given area.</p>
  
  @param decor Decoration to add
  @param index Position in the decoration chain to insert this decoration at. If this value
  is negative the decoration will be added at the end.