Linux Administration Guide, Appendix C, event variables - "required"

[RationalPolymer]

What is the meaning of "required" noted in the variable tables for any of the Events listed in the (Advanced LInux) Administrative/Administrator Guide, Appendix C? I can understand their possible necessity on a CLI posting function but don't see why they would be necessary in a Panel or CLI query/read function. Is "required" meant to imply that the Notification text MUST include these so-marked variables? What does it mean when an Event variable is marked as "required"?