The Kobo Formbuilder UI only presents a subset of the available functionality; this is also true for Formbuilder validation. However, you can still manually add whatever validation rules you like, you just need to know how to write the necessary constraint condition.
To validate only a maximum number of options are selected using just the Formbuilder try the following:
You must enter these ‘manual’ validation rules under here:
This functionality is available on all Kobo servers: global, EU, private or otherwise.
