Or can you declare it after you've seen the Attack result?
A few other questions:
Does a basic Defend action defend against all attacks until the player's next turn, or just one attack?
If an Ability just says, "until your next turn" as opposed to "until the start of your next turn", does this mean it lasts until the end of your next turn?
Chapter 2 describes a Reaction as happening "in response to a certain trigger" and each Reaction describes the conditions under which it is usable. So the real question is, does the "when you are attacked" style trigger come before or after the roll? Given that there are also triggers which say "when damaged" a super-strict reading would be that "when attacked" is when the attack is declared. That said, my group (who never stopped to actually consider the question) has basically been doing it after the roll, and it certainly doesn't break the game! So I'd say ask your GM.
OK cool.
By the way, does a basic Defend action defend against all attacks until the player's next turn, or just one attack?
Also, if an Ability just says, "until your next turn" as opposed to "until the start of your next turn", does this mean it lasts until the end of your next turn?
A Defend action lasts until it is used to block damage, or the start of it's creator's turn. Whichever comes first.
I don't believe so, for the second question. The effect wears off at 'your next turn', so it would wear off the moment your next turn starts.
There are some Abilities that do "Defend against all attacks."
Am I right in assuming that if the hero gets attacked multiple times that they can choose any one of those attacks to Defend
against? As opposed to being restricted to defending against the first attack against them.
Yup, which was what prompted my question.
There is no choice. From the core rulebook in chapter 2 it calls out it used up the next time you take damage and if you aren’t attacked by your next turn the effect expires. Some abilities will allow you to maintain a defend against all attacks on you until your next turn but the explicitly call it out. If an ability doesn’t state that and just has a defend effect on it then it works only against the next attack on you until your next turn. There is an option when using a Defend action to protect another hero instead but it again gets used up either by the next attack on that hero or until your next turn.
I don’t have access to the core rulebook, so thanks for clarifying.
Hopefully within a month the core rulebook should be publicly available.