Make field mandatory by checkbox, not by Due By or other non-obvious criteria.

This issue came to my attention when I found that the Participant Custom Field Multiselect box is always mandatory.  It doesn't matter if you have Due By/Visible By set to a value or not.  If you are using it, it is mandatory.  That is not how I want it to work. I have seen something similar on other fields where you put in validation, and it makes the field mandatory.  I don't necessarily want it to be mandatory, but if it is used, it should follow a certain format.  I would like to be able to specifically define if a field is mandatory or not.  It could be visible and not mandatory, visible and mandatory, and it may or may not have validation or selections.