Magic: The Gathering Comprehensive Rules Changes - Eventide to Shards of Alara

Old rule (Eventide)	New rule (Shards of Alara)
419.5b. [Click to view all changes.]
419.5b. Some abilities read, "you may [X]. If you do, [Y]." An "if you do" clause that follows a "you may [X]" clause refers to choosing to do the event X, regardless of what events actually occur as a result of that decision. If X is replaced entirely or in part by a different event, the "if you do" clause refers to the event that replaced X.

Old rule (Eventide)

New rule (Shards of Alara)

419.5b.

Some abilities read, "you may [X]. If you do, [Y]." An "if you do" clause that follows a "you may [X]" clause refers to choosing to do the event X, regardless of what events actually occur as a result of that decision. If X is replaced entirely or in part by a different event, the "if you do" clause refers to the event that replaced X.