Historical Rules · 22 July 2016
Rule 701.15b
Official source text from the 22 July 2016 Rules release
If a player is searching a hidden zone for cards with a stated quality, such as a card with a certain card type or color, that player isn’t required to find some or all of those cards even if they’re present in that zone. Example: Splinter says “Exile target artifact. Search its controller’s graveyard, hand, and library for all cards with the same name as that artifact and exile them. That player then shuffles his or her library.” A player casts Splinter targeting Howling Mine (an artifact). Howling Mine’s controller has another Howling Mine in her graveyard and two more in her library. Splinter’s controller must find the Howling Mine in the graveyard, but may choose to find zero, one, or two of the Howling Mines in the library.