Fires before a form submission is handled.
If you add one or more errors to the submission, the rest of the handling is skipped, essentially making the submission fail.
(awsmug\Torro_Forms\DB_Objects\Submissions\Submission) (Optional) Submission object.
(awsmug\Torro_Forms\DB_Objects\Forms\Form) (Optional) Form object.
(awsmug\Torro_Forms\DB_Objects\Forms\Container) (Optional) Current container object.
(array) (Optional) Submission POST data.