Historical Rules · 23 August 2019
Rule 901.11
Official source text from the 23 August 2019 Rules release
After the game has started, if a player moves the top card of their planar deck off that planar deck and turns it face up, that player has “planeswalked.” Continuous effects with durations that last until a player planeswalks end. Abilities that trigger when a player planeswalks trigger. See rule 701.23.