config/v1 package

IsUnspendable reports whether a fee or a royalty paid to who could never be paid out again: who is one of the realms listed above, which have no function for that, or it is not an address as the chain writes one, so no caller can ever present it. It is a check for such receivers only, not for the recipient of a transfer: the sales realm is on the list and rightly holds and moves ledger balances of its own.