What does the resupply and receive function do on the backpack

[unholywar23]

I have been looking around and messing with it but have no clue how it works can someone please explain this

 

[tedyhere]

Say you are building something with stone bricks and have a backpack full of stone bricks and only one stack in your hand. When you run out in your hand the backpack will autofill your hand with stone bricks from the backpack in resupply mode. I cannot remember what receive mode is.

 

[Antice]

when in receive mode the backpack will work in reverse when shift right clicking chests.
that is instead of emptying out into the chest it will fill itself up with valid items from the chest instead.
very usefull if you are building something big, and the back is emptying out fast, or of you just want to move a whole load of stuff at once.