NewFilter creates an filter that returns if a fork ID should be rejected or not based on the local chain's status.

NewID calculates the Ethereum fork ID from the chain config and head.

ErrLocalIncompatibleOrStale is returned by the validator if a remote fork checksum does not match any local checksum variation, signalling that the two chains have diverged in the past at some point (possibly at genesis).

ErrRemoteStale is returned by the validator if a remote fork checksum is a subset of our already applied forks, but the announced next fork block is not on our already passed chain.

ID is a fork identifier as defined by EIP-2124.