Every distinct wording since 2010, newest first.
July 12, 2019 · Core Set 2020
A player may activate a mana ability whenever they have priority, whenever they are casting a spell or activating an ability that requires a mana payment, or whenever a rule or effect asks for a mana payment (even in the middle of casting or resolving a spell or activating or resolving an ability).
June 18, 2010 · Archenemy
In an Archenemy game, the archenemy begins the game with a starting life total of 40 instead; see rule 904, "Archenemy."