diff --git a/core/modules/toolbar/js/toolbar.js b/core/modules/toolbar/js/toolbar.js
index d26b443..501c861 100644
--- a/core/modules/toolbar/js/toolbar.js
+++ b/core/modules/toolbar/js/toolbar.js
@@ -21,10 +21,11 @@ var orientation = JSON.parse(localStorage.getItem('Drupal.toolbar.trayOrientatio
 var locked = JSON.parse(localStorage.getItem('Drupal.toolbar.trayLocked')) || false;
 
 /**
- * Holds the jQuery objects of the toolbar DOM element and the trays.
+ * Holds the jQuery objects of the toolbar DOM element, the trays and messages.
  */
 var $toolbar;
 var $trays;
+var $messages;
 
 /**
  * Holds the mediaQueryList object.
@@ -47,6 +48,9 @@ Drupal.behaviors.toolbar = {
     var options = $.extend(this.options, drupalSettings.toolbar);
     $toolbar = $(context).find('#toolbar').once('toolbar');
     if ($toolbar.length) {
+      // Append a messages element for appending interaction updates for screen
+      // readers.
+      $messages = $(Drupal.theme('toolbarMessageBox')).appendTo($toolbar);
       // Store the trays in a scoped variable.
       $trays = $toolbar.find('.tray');
       $trays
@@ -99,6 +103,10 @@ Drupal.behaviors.toolbar = {
  * Toggle a toolbar tab and the associated tray.
  */
 Drupal.toolbar.toggleTray = function (event) {
+  var strings = {
+    opened: Drupal.t('opened'),
+    closed: Drupal.t('closed')
+  };
   var $tab = $(event.target);
   var name = $tab.attr('data-toolbar-tray');
   // Activate the selected tab and associated tray.
@@ -110,6 +118,15 @@ Drupal.toolbar.toggleTray = function (event) {
     // Toggle aria-pressed.
     var value = $tab.attr('aria-pressed');
     $tab.attr('aria-pressed', (value === 'false') ? 'true' : 'false');
+    // Append a message that a tray has been opened.
+    $messages.html(
+      Drupal.theme('toolbarTrayMessage',
+        Drupal.t('@tray tray @state.', {
+          '@tray': name,
+          '@state': (value === 'true') ? strings.closed : strings.opened
+        })
+      )
+    );
     // Store the active tab name or remove the setting.
     if ($tab.hasClass('active')) {
       localStorage.setItem('Drupal.toolbar.activeTab', JSON.stringify(name));
@@ -169,12 +186,14 @@ Drupal.toolbar.setHeight = function () {
  * Respond to configured media query applicability changes.
  */
 Drupal.toolbar.mediaQueryChangeHandler = function (mql) {
-  var orientation = (mql.matches) ? 'horizontal' : 'vertical';
-  changeOrientation(orientation);
-  // Adjust the body to accommodate trays.
-  setBodyState();
-  // Adjust the height of the toolbar.
-  Drupal.toolbar.setHeight();
+  if (!locked) {
+    var orientation = (mql.matches) ? 'horizontal' : 'vertical';
+    changeOrientation(orientation);
+    // Adjust the body to accommodate trays.
+    setBodyState();
+    // Adjust the height of the toolbar.
+    Drupal.toolbar.setHeight();
+  }
 };
 
 /**
@@ -257,4 +276,24 @@ Drupal.theme.toolbarOrientationToggle = function () {
     '</div></div>';
 };
 
+/**
+ * A region to post messages that a screen reading UA will announce.
+ *
+ * @return {String}
+ *   A string representing a DOM fragment.
+ */
+Drupal.theme.toolbarMessageBox = function () {
+  return '<div id="toolbar-messages" class="element-invisible" role="region" aria-live="polite"></div>';
+};
+
+/**
+ * Wrap a message string in a p tag.
+ *
+ * @return {String}
+ *   A string representing a DOM fragment.
+ */
+Drupal.theme.toolbarTrayMessage = function (message) {
+  return '<p>' + message + '</p>';
+};
+
 }(jQuery, Drupal, drupalSettings));