Historical Rules · 25 September 2020
Rule 400.2
Official source text from the 25 September 2020 Rules release
Public zones are zones in which all players can see the cards’ faces, except for those cards that some rule or effect specifically allow to be face down. Graveyard, battlefield, stack, exile, ante, and command are public zones. Hidden zones are zones in which not all players can be expected to see the cards’ faces. Library and hand are hidden zones, even if all the cards in one such zone happen to be revealed.