Class CheckboxGridValidation

// Add a checkbox grid item to a form and require one response per column.
const form = FormApp.openById('123abc');
const checkboxGridItem = form.addCheckboxGridItem();
checkboxGridItem.setTitle('Where did you celebrate New Years?')
    .setRows(['New York', 'San Francisco', 'London'])
    .setColumns(['2014', '2015', '2016', '2017']);
const checkboxGridValidation = FormApp.createCheckboxGridValidation()
                                   .setHelpText('Select one item per column.')
                                   .requireLimitOneResponsePerColumn()
                                   .build();
checkboxGridItem.setValidation(checkboxGridValidation);