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

In this case, try this out:

In the survey tab of your xlsform:

In the choices tab of your xlsform:

Image 2

Data entry screen as seen in Enketo: when a condition is met

Data entry screen as seen in Enketo: when a condition is met

Data entry screen as seen in Enketo: when a condition is not met

Data entry screen as seen in Enketo: when a condition is not met

Reference xlsform:

Constraint.xlsx (11.4 KB)