A group of foldable containers that doesn't allow more than one container to be expanded at a time. A group of [FoldableContainer]-derived nodes. Only one container can be expanded at a time. Returns an [Array] of [FoldableContainer]s that have this as their FoldableGroup (see [member FoldableContainer.foldable_group]). This is equivalent to [ButtonGroup] but for FoldableContainers. Returns the current expanded container. If [code]true[/code], it is possible to fold all containers in this FoldableGroup. Emitted when one of the containers of the group is expanded.