 <script>
          window.addDemoReadyListener('#customizing-filtering', function(document) {
            const comboBox = document.querySelector('vaadin-combo-box');

            // NOTE: elements is an array of the form {'Carbon', ...}
            comboBox.filteredItems = elements;

            comboBox.addEventListener('filter-changed', function(e) {
              comboBox.filteredItems = elements.filter(function(item) {
                return item.indexOf(e.detail.value) === 0;
              });
      