CollapseViewHelper blocks collapsing of nested containers

[EvilBMP]

Right now, the CollapseViewHelper has the following condition:

collapse/Classes/ViewHelpers/CollapseViewHelper.php

Line 36 in 7117a86

if ($type instanceof GridColumnItem && !$type instanceof ContainerGridColumnItem) {

Why is the type ContainerGridColumnItem forbidden here? This blocks the ability to collapse container elements inside another container element.

Is this by design or a bug?

IMHO this condition should be if ($type instanceof GridColumnItem || $type instanceof ContainerGridColumnItem) {

I can provide a PR but wanted to discuss this first. Thanks.