Labour's Kim Leadbeater announced as winner in Batley by-election

The transcript discusses various aspects of an election process, including voter entitlement, identification through marks, criteria for valid ballots, and the number of rejected ballots. It concludes with the declaration of Kim Michelle Leadbeater as the duly elected candidate.

What is the significance of the writing or mark by which a voter could be identified?

What does the phrase 'I do hereby declare that' imply in the context of the election?