The opt-in full Replace-by-Fee (opt-in full-RBF) signaling policy described in BIP-125 allows spenders to add a signal to a transaction indicating that they want to be able to replace that transaction in the future.
In response to this signal,
Nodes may allow transactions containing this signal to be replaced in their mempools.
The recipient or recipients of a transaction containing this signal may choose not to treat it as payment until it has been confirmed, eliminating the risk that the spender will use allowed replacements to defraud them.
This policy specifies two ways a transaction can signal that it is replaceable.
Explicit signaling: A transaction is considered to have opted in to allowing replacement of itself if any of its inputs have an nSequence number less than (0xffffffff - 1).
Inherited signaling: Transactions that don't explicitly signal replaceability are replaceable under this policy for as long as any one of their ancestors signals replaceability and remains unconfirmed.
