Type Alias Justification 

pub type Justification = Vec<u8>;

An abstraction over justification for a block’s validity under a consensus algorithm.

Essentially a finality proof. The exact formulation will vary between consensus algorithms. In the case where there are multiple valid proofs, inclusion within the block itself would allow swapping justifications to change the block’s hash (and thus fork the chain). Sending a Justification alongside a block instead bypasses this problem.

Aliased Type

pub struct Justification { /* private fields */ }