Some tangentially related thoughts on triggers in Dominion, when resolving other triggered abilities first...
The red ones don't currently exist in Dominion.
1) While this is in play, when you gain a card, +1 VP.
This triggers if it's in play, and also if it enters play from another when-gain ability. When you resolve it, you get +1 VP whether it's still in play or not.
2) When you gain a card, if this is in play, +1 VP.
This triggers whether it's in play or not. When you resolve it, you only get +1 VP if it's in play then.
3) When you gain a card with this in play, +1 VP.
This only triggers if it's in play right then. When you resolve it, you get +1 VP whether it's still in play or not.
Equivalent triggers for checking if you have $:
1) While you have $2, when you gain a card, +1 VP. [This is weird of course, but should work like this]
This triggers if you have $2 or if you get $2 from another when-gain. When you resolve it, you get +1 VP no matter what.
2) When you gain a card, if you have $2, +1 VP.
This triggers no matter what. When you resolve it, you only get +1 VP if you have $2 then.
3) When you gain a card with $2 left, +1 VP.
This only triggers if you have $2 right then. When you resolve it, you get +1 VP no matter what.
Equivalent triggers for checking the type (was relevant with old BoM and Inheritance):
1) While a card is an Action card, when you gain it, +1 VP. [Even weirder, but should work like this]
This triggers if you gain an Action or if you gain a card that gets the Action type from another when-gain. When you resolve it, you get +1 VP no matter what.
2) When you gain a card, if it's an Action, +1 VP.
This triggers no matter what. When you resolve it, you only get +1 VP if the gained card is an Action then.
3) When you gain an Action card, +1 VP.
This only triggers if you gain a card that is an Action right then. When you resolve it, you get +1 VP no matter if the card is still an Action.