Minor comment typo "iff" instead of "if", spotted while going over the RBF implementation in 0.15, still present in master. Typo introduced in the commit below.
https://github.com/bitcoin/bitcoin/pull/10706/commits/2fffaa97381f741786fff2e6ff25f4b9a74037fe
Please pull or add to list of typos to correct.
iff is not a typo it's common CS/math lingo that means "if and only if" (well, to be honest I don't know for sure if it's a typo in this case, but I'd have read it like that at least …)
The logic proceeding the comment seems to be the only place where the conservative bool to estimateSmartFee would default to false based on RBF, so the mathematical use of iff would seem correct.