The status key of the task. Set this to a cancelled-category status to cancel the task. A task in a done-category status can be moved again: moving it to a status that reopens the task (anything outside the done and cancelled categories) clears completed_at, while moving it to a second done-category status or cancelling it keeps the original completion date. Cancelling is final: a task in a cancelled-category status cannot be transitioned again.
