FSA Annual Pledge vs Employee Contribution Override

Hello - Can someone explain how the Annual Pledge field and Employee Contribution Override work together in Base Benefits or don't they? Should only one be used? It appears that if an EE Override amount is entered, it can exceed the Annual Pledge if they both exist. If only Annual Pledge is used, will the system auto adjust the final deduction of the year to meet the Annual Pledge exactly (if the annual pledge amount is rounded based on number of pay periods)? PeopleBooks does not provide much detail on these fields, so any additional information experts may have would