private void RemovePlacement(InstanceHolder holder, int index)
        {
            var element = holder.Elements[index];

            if (element == null)
            {
                return;
            }

            holder.GroupElement.Children.Remove(element);
            element.Dispose();
            holder.Elements[index] = null;
        }
        private void ConfigurePlacement(InstanceHolder holder, int index)
        {
            RemovePlacement(holder, index);

            var placement = holder.Placements[index];

            var inst = factory.CreateModelSection(tagId, 0, placement.MeshIndex, 1);

            if (inst == null)
            {
                holder.Elements[index] = null;
                return;
            }

            BindPlacement(placement, inst);

            holder.Elements[index] = inst;
            holder.GroupElement.Children.Add(inst);
        }