What are the absence rules alert levels?

Absence rules can be given a strength which determines how they behave when they are breached

A mandatory rule will not be able to be sent for approval.  A mandatory rule with override is able to be sent for approval. A rule with Warn only will highlight the conflict to the employee & manager.  This gives three levels of controls: can't ever happen, preferably doesn't ever happen (but can be a little flexible) and Managers discretion to approve.