How is the syntax for one selected answer where another answer must also be selected in a select_multiple question?

[Kal_Lam]

You could do the same as outlined in the image below:

In the survey tab of your xlsform:

In the choices tab of your xlsform:

Data entry screen as seen in Enketo: when conditions are not met

Data entry screen as seen in Enketo: when conditions are met

Reference xlsform:

Constraint.xlsx (11.4 KB)