This is currently not possible, but I like the idea to use a custom list with it's entries for validation to specify that e.g. a value matching one of the list values must be provided.But you can kinda work around this maybe:- Create a custom list- Create a custom form- Add the custom list to one of the form fields- Change the visibility to "required" or something else that requires the user to specify a value - Save the custom form -> The "config" button will now appear behind the form field with the custom list- Click on the "config" button and choose "Typeahead" instead of "Dropdown"Or use a "short answer" field with the validator "custom (regex)" and specify a regex for all the product serials - but depending on the amount of serials, the first solution is maybe the better one ;)