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For example, imagine you have two questions

Question ID
Question Text
/data/colorWhat is your favorite color?
/data/foodWhat is your favorite food?

In this scenario you want the user to answer exactly one of  of these, though the user can answer either one.


The simplest solution would be to add a question beforehand which asks:

Question ID
Question Text

Which question do you want to answer?

  • What is your favorite color?
  • What is your favorite food?


2. Create a Label after the Questions, but  but still in the Question List Group


You will want the display condition to show the label when you don't answer exactly one of them. For example:

(#form/data/color != '' and #form/data/food != '') or (#form/data/color = '' and #form/data/food = '')

4. Set the Label's Validation Condition

We want to treat the label like a validation condition so put a validation condition that can never be met. For example:


Set the label's validation message to be: "You must answer exactly one of the above questions."

Now when the user doesn't answer exactly one question they will see an error message which prevents them from going forward until they correct it.