ApplyDAOHardFork modifies the state database according to the DAO hard-fork rules, transferring all balances of a set of DAO accounts to a single refund contract.

VerifyDAOHeaderExtraData validates the extra-data field of a block header to ensure it conforms to DAO hard-fork rules.

VerifyGaslimit verifies the header gas limit according increase/decrease in relation to the parent gas limit.

ErrBadNoDAOExtra is returned if a header does support the DAO fork on a no- fork client.

ErrBadProDAOExtra is returned if a header doesn't support the DAO fork on a pro-fork client.