diff --git a/h5p.classes.php b/h5p.classes.php
index 71e95c4..851515f 100644
--- a/h5p.classes.php
+++ b/h5p.classes.php
@@ -2898,7 +2898,12 @@ class H5PContentValidator {
 
     // Check if string is within allowed length
     if (isset($semantics->maxLength)) {
-      $text = mb_substr($text, 0, $semantics->maxLength);
+      if (!extension_loaded('mbstring')) {
+        $this->h5pF->setErrorMessage($this->h5pF->t('The mbstring PHP extension is not loaded. H5P need this to function properly'), 'error');
+      }
+      else {
+        $text = mb_substr($text, 0, $semantics->maxLength);
+      }
     }
 
     // Check if string is according to optional regexp in semantics
@@ -2948,7 +2953,11 @@ class H5PContentValidator {
         // file name, 2. testing against a returned error array that could
         // never be more than 1 element long anyway, 3. recreating the regex
         // for every file.
-        if (!preg_match($wl_regex, mb_strtolower($file))) {
+        if (!extension_loaded('mbstring')) {
+          $this->h5pF->setErrorMessage($this->h5pF->t('The mbstring PHP extension is not loaded. H5P need this to function properly'), 'error');
+          $valid = FALSE;
+        }
+        else if (!preg_match($wl_regex, mb_strtolower($file))) {
           $this->h5pF->setErrorMessage($this->h5pF->t('File "%filename" not allowed. Only files with the following extensions are allowed: %files-allowed.', array('%filename' => $file, '%files-allowed' => $whitelist)), 'error');
           $valid = FALSE;
         }
diff --git a/js/h5p-confirmation-dialog.js b/js/h5p-confirmation-dialog.js
index c948192..a06166b 100644
--- a/js/h5p-confirmation-dialog.js
+++ b/js/h5p-confirmation-dialog.js
@@ -17,6 +17,10 @@ H5P.ConfirmationDialog = (function (EventDispatcher) {
     EventDispatcher.call(this);
     var self = this;
 
+    // Make sure confirmation dialogs have unique id
+    H5P.ConfirmationDialog.uniqueId += 1;
+    var uniqueId = H5P.ConfirmationDialog.uniqueId;
+
     // Default options
     options = options || {};
     options.headerText = options.headerText || H5P.t('confirmDialogHeader');
@@ -44,6 +48,16 @@ H5P.ConfirmationDialog = (function (EventDispatcher) {
       e.preventDefault();
     }
 
+    /**
+     * Flow focus to element
+     * @param {HTMLElement} element Next element to be focused
+     * @param {Event} e Original tab event
+     */
+    function flowTo(element, e) {
+      element.focus();
+      e.preventDefault();
+    }
+
     // Offset of exit button
     var exitButtonOffset = 2 * 16;
     var shadowOffset = 8;
@@ -59,7 +73,15 @@ H5P.ConfirmationDialog = (function (EventDispatcher) {
     // Create outer popup
     var popup = document.createElement('div');
     popup.classList.add('h5p-confirmation-dialog-popup', 'hidden');
+    popup.setAttribute('role', 'dialog');
+    popup.setAttribute('aria-labelledby', 'h5p-confirmation-dialog-dialog-text-' + uniqueId);
     popupBackground.appendChild(popup);
+    popup.addEventListener('keydown', function (e) {
+      if (e.which === 27) {// Esc key
+        // Exit dialog
+        dialogCanceled(e);
+      }
+    });
 
     // Popup header
     var header = document.createElement('div');
@@ -81,6 +103,7 @@ H5P.ConfirmationDialog = (function (EventDispatcher) {
     var text = document.createElement('div');
     text.classList.add('h5p-confirmation-dialog-text');
     text.innerHTML = options.dialogText;
+    text.id = 'h5p-confirmation-dialog-dialog-text-' + uniqueId;
     body.appendChild(text);
 
     // Popup buttons
@@ -92,41 +115,66 @@ H5P.ConfirmationDialog = (function (EventDispatcher) {
     var cancelButton = document.createElement('button');
     cancelButton.classList.add('h5p-core-cancel-button');
     cancelButton.textContent = options.cancelText;
-    cancelButton.onclick = dialogCanceled;
-    cancelButton.onkeydown = function (e) {
-      if (e.which === 32) { // Space
-        dialogCanceled(e);
-      }
-    };
-    buttons.appendChild(cancelButton);
 
     // Confirm button
     var confirmButton = document.createElement('button');
     confirmButton.classList.add('h5p-core-button',
       'h5p-confirmation-dialog-confirm-button');
     confirmButton.textContent = options.confirmText;
-    confirmButton.onclick = dialogConfirmed;
-    confirmButton.onkeydown = function (e) {
-      if (e.which === 32) { // Space
-        dialogConfirmed(e);
-      }
-    };
-    buttons.appendChild(confirmButton);
 
     // Exit button
     var exitButton = document.createElement('button');
     exitButton.classList.add('h5p-confirmation-dialog-exit');
-    exitButton.onclick = dialogCanceled;
-    exitButton.onkeydown = function (e) {
+    exitButton.setAttribute('aria-hidden', 'true');
+    exitButton.tabIndex = -1;
+    exitButton.title = options.cancelText;
+
+    // Cancel handler
+    cancelButton.addEventListener('click', dialogCanceled);
+    cancelButton.addEventListener('keydown', function (e) {
       if (e.which === 32) { // Space
         dialogCanceled(e);
       }
-    };
+      else if (e.which === 9 && e.shiftKey) { // Shift-tab
+        flowTo(confirmButton, e);
+      }
+    });
+    buttons.appendChild(cancelButton);
+
+    // Confirm handler
+    confirmButton.addEventListener('click', dialogConfirmed);
+    confirmButton.addEventListener('keydown', function (e) {
+      if (e.which === 32) { // Space
+        dialogConfirmed(e);
+      }
+      else if (e.which === 9 && !e.shiftKey) { // Tab
+        flowTo(cancelButton, e);
+      }
+    });
+    buttons.appendChild(confirmButton);
+
+    // Exit handler
+    exitButton.addEventListener('click', dialogCanceled);
+    exitButton.addEventListener('keydown', function (e) {
+      if (e.which === 32) { // Space
+        dialogCanceled(e);
+      }
+    });
     popup.appendChild(exitButton);
 
     // Wrapper element
     var wrapperElement;
 
+    // Focus capturing
+    var focusPredator;
+
+    // Maintains hidden state of elements
+    var wrapperSiblingsHidden = [];
+    var popupSiblingsHidden = [];
+
+    // Element with focus before dialog
+    var previouslyFocused;
+
     /**
      * Set parent of confirmation dialog
      * @param {HTMLElement} wrapper
@@ -137,6 +185,87 @@ H5P.ConfirmationDialog = (function (EventDispatcher) {
       return this;
     };
 
+    /**
+     * Capture the focus element, send it to confirmation button
+     * @param {Event} e Original focus event
+     */
+    var captureFocus = function (e) {
+      if (!popupBackground.contains(e.target)) {
+        e.preventDefault();
+        confirmButton.focus();
+      }
+    };
+
+    /**
+     * Hide siblings of element from assistive technology
+     *
+     * @param {HTMLElement} element
+     * @returns {Array} The previous hidden state of all siblings
+     */
+    var hideSiblings = function (element) {
+      var hiddenSiblings = [];
+      var siblings = element.parentNode.children;
+      var i;
+      for (i = 0; i < siblings.length; i += 1) {
+        // Preserve hidden state
+        hiddenSiblings[i] = siblings[i].getAttribute('aria-hidden') ?
+          true : false;
+
+        if (siblings[i] !== element) {
+          siblings[i].setAttribute('aria-hidden', true);
+        }
+      }
+      return hiddenSiblings;
+    };
+
+    /**
+     * Restores assistive technology state of element's siblings
+     *
+     * @param {HTMLElement} element
+     * @param {Array} hiddenSiblings Hidden state of all siblings
+     */
+    var restoreSiblings = function (element, hiddenSiblings) {
+      var siblings = element.parentNode.children;
+      var i;
+      for (i = 0; i < siblings.length; i += 1) {
+        if (siblings[i] !== element && !hiddenSiblings[i]) {
+          siblings[i].removeAttribute('aria-hidden');
+        }
+      }
+    };
+
+    /**
+     * Start capturing focus of parent and send it to dialog
+     */
+    var startCapturingFocus = function () {
+      focusPredator = wrapperElement.parentNode || wrapperElement;
+      focusPredator.addEventListener('focus', captureFocus, true);
+    };
+
+    /**
+     * Clean up event listener for capturing focus
+     */
+    var stopCapturingFocus = function () {
+      focusPredator.removeAttribute('aria-hidden');
+      focusPredator.removeEventListener('focus', captureFocus, true);
+    };
+
+    /**
+     * Hide siblings in underlay from assistive technologies
+     */
+    var disableUnderlay = function () {
+      wrapperSiblingsHidden = hideSiblings(wrapperElement);
+      popupSiblingsHidden = hideSiblings(popupBackground);
+    };
+
+    /**
+     * Restore state of underlay for assistive technologies
+     */
+    var restoreUnderlay = function () {
+      restoreSiblings(wrapperElement, wrapperSiblingsHidden);
+      restoreSiblings(popupBackground, popupSiblingsHidden);
+    };
+
     /**
      * Fit popup to container. Makes sure it doesn't overflow.
      * @params {number} [offsetTop] Offset of popup
@@ -167,7 +296,11 @@ H5P.ConfirmationDialog = (function (EventDispatcher) {
      * @returns {H5P.ConfirmationDialog}
      */
     this.show = function (offsetTop) {
+      // Capture focused item
+      previouslyFocused = document.activeElement;
       wrapperElement.appendChild(popupBackground);
+      startCapturingFocus();
+      disableUnderlay();
       popupBackground.classList.remove('hidden');
       fitToContainer(offsetTop);
       setTimeout(function () {
@@ -199,6 +332,11 @@ H5P.ConfirmationDialog = (function (EventDispatcher) {
     this.hide = function () {
       popupBackground.classList.add('hiding');
       popup.classList.add('hidden');
+
+      // Restore focus
+      stopCapturingFocus();
+      previouslyFocused.focus();
+      restoreUnderlay();
       setTimeout(function () {
         popupBackground.classList.add('hidden');
         wrapperElement.removeChild(popupBackground);
@@ -214,3 +352,5 @@ H5P.ConfirmationDialog = (function (EventDispatcher) {
   return ConfirmationDialog;
 
 }(H5P.EventDispatcher));
+
+H5P.ConfirmationDialog.uniqueId = -1;
diff --git a/js/h5p-data-view.js b/js/h5p-data-view.js
index 0edfc56..89080e0 100644
--- a/js/h5p-data-view.js
+++ b/js/h5p-data-view.js
@@ -288,6 +288,11 @@ var H5PDataView = (function ($) {
     var self = this;
 
     if (self.pagination === undefined) {
+      if (self.table === undefined) {
+        // No table, no pagination
+        return;
+      }
+
       // Create new widget
       var $pagerContainer = $('<div/>', {'class': 'h5p-pagination'});
       self.pagination = new H5PUtils.Pagination(num, self.limit, function (offset) {
diff --git a/js/h5p.js b/js/h5p.js
index 5a1c9e1..5de66e2 100644
--- a/js/h5p.js
+++ b/js/h5p.js
@@ -122,13 +122,15 @@ H5P.init = function (target) {
         delete contentData.contentUserData;
         var dialog = new H5P.Dialog('content-user-data-reset', 'Data Reset', '<p>' + H5P.t('contentChanged') + '</p><p>' + H5P.t('startingOver') + '</p><div class="h5p-dialog-ok-button" tabIndex="0" role="button">OK</div>', $container);
         H5P.jQuery(dialog).on('dialog-opened', function (event, $dialog) {
-          $dialog.find('.h5p-dialog-ok-button').click(function () {
-            dialog.close();
-          }).keypress(function (event) {
-            if (event.which === 32) {
+
+          var closeDialog = function (event) {
+            if (event.type === 'click' || event.which === 32) {
               dialog.close();
+              H5P.deleteUserData(contentId, 'state', 0);
             }
-          });
+          };
+
+          $dialog.find('.h5p-dialog-ok-button').click(closeDialog).keypress(closeDialog);
         });
         dialog.open();
       }