If used to cancel a strike, another strike is chosen.

Can be used to cancel a card played at the end of a round (eg. Disarm) or "when combat would end" (eg. Psyche!): it then counts as having been played during that ending round.

Cards are not replaced during the "as played" window. The cancelation must be played immediately: no other effects can be used, except for wakes (eg. neither The Barrens nor Dreams of the Sphinx can be used).

If the canceled card had a "do not replace until" clause (or alternate replacement like Steely Tenacity), that clause is canceled as well and the card is replaced normally.

The canceled card has still been played. The same reaction or modifier cannot be played again by the same minion. Any card which text prohibits to play more than once cannot be played again.

If a limited effect is canceled (bleed, additional strike), then the limit is not triggered and another limited effect can be used.

A card played "as if from hand" can be canceled "as played"