Custom Validation for Side by Side Question - Only allow one column to be answered

@Chrissy So if I understand correctly, you want the respondent to choose _only_ "Required", "Preferred", or Optional. I would actually render the question differently so that it's clearer for the respondent, because from the respondent's point of view, if I see a matrix question, my impulse is to respond to all three columns. Instead, I would break this into two questions (for the user experience -- in your survey it will show up as four) Question A: Something to the effect of is _x_ Required, Preferred or Optional. Then set up display logic so that each of the following three questions is displayed if the respondent chooses each option in Question A. Question B: "You chose 'Required'. How would you rank the following options: 4 Gas Monitor, etc. Questions C and D would follow with similar language for the 'Preferred' or 'Optional' choices. In this way, it's a much clearer respondent experience and you're also more likely to not run into accessibility issues. Hope this helps, Adam