Historical Rules · 20 November 2020
Rule 901.11
Official source text from the 20 November 2020 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 701.24.