Minecraft wiki entry for destroy, associated text: Specifies the direction of Agent to destroy.
Must be one of:
forward to destroy block/item on the front.
back to destroy block/item on the back.
left to destroy block/item on the left-hand side.
right to destroy block/item on the right-hand side.
up to destroy block/item on the top-hand side.
down to destroy block/item on the bottom-hand side.