Historical Rules · 18 June 2010
Rule 711.4b
Official source text from the 18 June 2010 Rules release
The controller of another player's turn can't make choices or decisions for that player that aren't called for by the rules or by any objects. The controller also can't make any choices or decisions for the player that would be called for by the tournament rules. Example: The player whose turn is being controlled still chooses whether he or she leaves to visit the restroom, trades a card to someone else, takes an intentional draw, or calls a judge about an error or infraction.