10/4/2004: You must assign at least 1 damage to each target.
10/4/2004: You can't choose zero targets. You must choose at least one target.
9/25/2006: The opponent targeted for the life gain effect may also have been targeted by the damage effect. If this happens and the damage effect drops that player's life total to 0 or less, the life gain effect will raise his or her life total above 0 again before the player would lose the game.