Constraint on select_multiple answers

[Nicole_Ueberschär]

I wonder how I can check on not allowed combinations of select_multiple answers. 

For example: I have a list of multiple choices (category): none, covered, uncovered, vip. If none is checked, the others should not be applicable, for the others any combination is possible. It seems awkward to list all possible combinations as a constraint.

I was thinking of something like  if(selected(${category},'None') then count(${category}) has to be 1 but how do I put this as a constraint?

Thanks in advance!

[MatFeltner]

To J. Tedrick: yes, by 'real-time' I meant an immediate response instated f waiting til validation.

To J. Moore: The note option is helpful (and I have now used that for other messages) -

Thanks to responses

Dudley's response under a different GeoNet login