I'm hoping someone can help me out here. In compiling the complete rules for Dominion, I've written down the following rule.
A) When several abilities happen at the same time, after determining the order of the abilities, resolve all of them, even if the condition that triggered an ability changes before that ability is resolved.
There's also a second part:
B) However, if an ability refers to a card which is no longer defined (for instance a "gained card" that wasn't gained after all), then that ability can't be carried out.
But it's the first part (A) I'm concerned with now, and specifically the bolded part. It's a rule I've been having in my head, but I can't source it to anything official. I know of several posts by forum members where it's mentioned. But what I'm after is a post where Donald refers to the rule, or any place in any rulebook where it's implicit (since I doubt that it's explicitly stated anywhere), or any ruling by Donald where it's implicit.
I'm even having a hard time thinking of examples where it would apply. But I managed to come up with one: I buy a Mandarin with Royal Seal in play. Royal Seal's when-gain triggers because it's in play. I elect to resolve the Mandarin's when-gain first, putting all Treasures on top of my deck. Then I resolve Royal Seal's when-gain even though it's no longer in play, and put the Mandarin on the deck. According to this rule, this is allowed. On isotropic it also works.
So I want to confirm that the above is correct, and that the rule is correct. And any other examples where it would apply would be greatly appreciated.