Help, what does the "Change Box" keybind option do in the controls menu?

[Aeglefire]

If you go into the Options menu and go into the Controls menu, there's this keybind setting called "Change Box". What does it do? I've tried setting the keybind to "j" but it doesn't do anything in-game when I press "j". I've attached a picture:

[zenburu]

It moves the selected item between your inventory and your backpack/chest/fridge, it's the same as pressing shift+click