Subrule · Chapter 1
cr:1.8.5a
Only public objects in the arena or on the stack are targetable (can be selected as a legal target), unless the effect specifies the legal target as a zone or an object that does not exist in the arena or on the stack. If the effect specifies the legal target as an object in a public zone, only public objects in that zone targetable, unless stated otherwise.
Example: Memorial Ground has the text “Put target attack action card with cost 2 or less from your graveyard on top of your deck.” which describes a legal target as a card in the graveyard as opposed to a card in the arena or on the stack. The graveyard is a public zone, so only public (face-up) cards in the graveyard can be chosen as a legal target.