The second paragraph in the "overview" section starts talking about the "SE" but this term is never defined. It is unclear what this is.

A statecoin is a specific amount of Bitcoin that has been deposited to an address where the corresponding private key is split between the depositor and the Mercury server (or 'statechain entity') and the depositor holds a time-locked 'backup transaction' that allows them to claim full control of the coin after a specified locktime. The full private key of the statecoin is never known by any party, and both the owner and the statechain entity must cooperate to sign a transaction.