Historical Rules · 1 October 2012
Rule 901.4
Official source text from the 1 October 2012 Rules release
At the start of the game, each player shuffles his or her planar deck so that the cards are in a random order. Each deck is placed face down next to its owner's library. All plane and phenomenon cards remain in the command zone throughout the game, both while they're part of a planar deck and while they're face up.