Technically `0x1` will signal opt-in RBF (since 0x1 ≤ 0xFFFFFFFD); however it also sets a relative timelock of 1 block. This seems like an unintended bug. It also fingerprints cake wallet since `0x1` is an abnormal value. This is especially harmful in collaborative settings e.g payjoin. Most wallets set `nsequence = 0xFFFFFFFD` to opt into RBF or just use full rbf which seems to be gaining more adoption.
