Block struct
A block block = [ header , transaction_bodies : [* transaction_body] , transaction_witness_sets : [* transaction_witness_set] , transaction_metadata_set : { * transaction_index => transaction_metadata } ]; Valid blocks must also satisfy the following two constraints: ; 1) the length of transaction_bodies and transaction_witness_sets ; must be the same ; 2) every transaction_index must be strictly smaller than the ; length of transaction_bodies.