It supports all corner cases:
- The UI doesn't allow to put a shulker box into another shulker box
- The shulker box can be moved between slots inside of your inventory while it is open
- Dropping the shulker box (moving it outside the inventory or pressing Q) while it's open will save its contents
- Swapping items with the hotbar (pressing 1-9 while hovering over a slot)
- Shift-click
- Shift-double-click
- Dragging items and item stacks through your inventory and the opened shulker box
The shulker box can be opened when right-clicking while holding it in the main hand, and placed when right-clicking while sneaking.
This can be reversed by setting open-while-sneaking in the config file to true.
To be able to open a shulker box, a player requires the permission openshulkerbox.open.