It is designed to be easily removable and taken out off the fridge to sort sort/add/remove things from the box. It was made according to the dimensions of a popular spice packet but anything can be stored in this easily accessible tray/box, like medicine, small form factor sauce bottles and so on.

Not sure about fridge door shelve dimensions on other brands, but this was made for Samsung fridge. As walls are somewhat thick in this model, it could be scaled down accordingly if needed.