Historical Rules · 1 February 2010
Rule 109.5
Official source text from the 1 February 2010 Rules release
The words "you" and "your" on an object refer to the object's controller, its would-be controller (if a player is attempting to cast or activate it), or its owner (if it has no controller). For a static ability, this is the current controller of the object it's on. For an activated ability, this is the player who activated the ability. For a triggered ability, this is the controller of the object when the ability triggered, unless it's a delayed triggered ability. For a delayed triggered ability, this is the controller of the spell or ability that created it.