private static void SelectByTextOrValueMultiple(this SelectList selectList, Constraint constraint) { // This is copied from SelectList.SelectMultiple var options = selectList.Options.Filter(constraint); if (options.Count == 0) { throw new SelectListItemNotFoundException(constraint.ToString(), selectList); } foreach (var option in options) { if (option.Selected) { continue; } option.SetAttributeValue("selected", "true"); } selectList.FireEvent("onchange"); }