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