Historical Rules · 1 October 2012
Rule 406.3
Official source text from the 1 October 2012 Rules release
Exiled cards are, by default, kept face up and may be examined by any player at any time. Cards "exiled face down" can't be examined by any player except when instructions allow it. A card exiled face down has no characteristics, but the spell or ability that exiled it may allow it to be cast from exile. Unless that card is being cast face down (see rule 707.4), the card is turned face up just before the player announces that he or she is casting the spell (see rule 601.2).