106.4. The Facedown Zones
106.4.a. Each Battlefield is associated with a sub-zone called a Facedown Zone , a single logical space that a card can be put facedown in through various Game Effects.
106.4.b. Each Facedown Zone has a maximum occupancy of one card.
106.4.c. Cards can only be placed in or occupy the Facedown Zone if the controller of the card also controls the associated Battlefield.
106.4.d. If the Hidden card's controller loses Control of the Battlefield , the card in the Facedown Zone is removed during the next Cleanup. See rule 318. Cleanups for more information. See rule 408. Hide for more information.
106.4.e. Facedown Zones are not locations.