-changed="_updateValue">[[_getLabel(item)]]</vaadin-checkbox>
    </template>

  </template>
  <script>
    (function() {
      /**
       * @memberof ExpenseManager
       */
      class OptionGroupElement extends Polymer.Element {
        static get is() {
          return 'option-group';
        }

        static get properties() {
          return {
            /**
             * The list of available options.
             * @type {Array<object|string>}
             */
            items: Array,

       