Text (US+errata): Whenever another card is put into a graveyard from anywhere, exile that card. [Oracle 2009/07/08]
The card does go to the graveyard before it is removed from the game, so other triggered abilities like Energy Field will trigger on the card going to the graveyard. [D'Angelo 1999/01/12]
It will not trigger on itself going to the graveyard from play. [D'Angelo 2008/07/12]
It will trigger on any cards going to the graveyard at the same time it does, and it will remove them from the game. [D'Angelo 1999/03/06]
If Disenchant is used on it, Planar Void goes to the graveyard, then Disenchant goes to the graveyard and stays there. [DeLaney 1999/01/18]
