Class CheckboxValidationBuilder

// Add a checkBox item to a form and require exactly two selections.
constform=FormApp.create('My Form');
constcheckBoxItem=form.addCheckboxItem();
checkBoxItem.setTitle('What two condiments would you like on your hot dog?');
checkBoxItem.setChoices([
checkBoxItem.createChoice('Ketchup'),
checkBoxItem.createChoice('Mustard'),
checkBoxItem.createChoice('Relish'),
]);
constcheckBoxValidation=FormApp.createCheckboxValidation()
.setHelpText('Select two condiments.')
.requireSelectExactly(2)
.build();
checkBoxItem.setValidation(checkBoxValidation);