Every distinct wording since 2010, newest first.
June 18, 2021 · Modern Horizons 2
An object’s ability that allows a player to pay an alternative cost rather than its mana cost or otherwise modifies what that particular object costs to cast functions on the stack.
July 12, 2019 · Core Set 2020
An object’s ability that restricts or modifies how that particular object can be played or cast functions in any zone from which it could be played or cast and also on the stack. An object’s ability that grants it another ability that restricts or modifies how that particular object can be played or cast functions only on the stack.