Update to Drupal 8.1.0. For more information, see https://www.drupal.org/drupal-8.1.0-release-notes

core/misc/collapse.js

@@ -13,6 +13,7 @@
    * @constructor Drupal.CollapsibleDetails
    *
    * @param {HTMLElement} node
+   *   The details element.
    */
   function CollapsibleDetails(node) {
     this.$node = $(node);
@@ -82,6 +83,7 @@
      * Handle legend clicks.
      *
      * @param {jQuery.Event} e
+     *   The event triggered.
      */
     onLegendClick: function (e) {
       this.toggle();
@@ -120,6 +122,9 @@
    * Polyfill HTML5 details element.
    *
    * @type {Drupal~behavior}
+   *
+   * @prop {Drupal~behaviorAttach} attach
+   *   Attaches behavior for the details element.
    */
   Drupal.behaviors.collapse = {
     attach: function (context) {