Section 15.1.2 says you can have both dfdl:choiceBranchKey and a discriminator on a choice branch. But it doesn't clarify what the meaning of having both is.
My assumption is that if you have both, the choice is resolved by the choiceDispatchKey/choiceBranchKey, so any discriminator would be about some surrounding point of uncertainty outside the choice.
I wanted to confirm this is the intention.