I want to spend some time improving best practice rules. For DAX expression validations, they should also apply to functions (probably higher severity as well as we don't want to reuse non-optimal code). I see that I don't find Functions on the list on Apply to, as I assume I need to modify it there, and not in the rule itself. As an example for unqualified column rererences:
DependsOn.Any(Key.ObjectType = "Column" and Value.Any(not FullyQualified))