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(function (global, factory) {
  typeof exports === 'object' && typeof module !== 'undefined' ? factory() :
  typeof define === 'function' && define.amd ? define('inert', factory) :
  (factory());
}(this, (function () { 'use strict';

  var _createClass = function () { function defineProperties(target, props) { for (var i = 0; i < props.length; i++) { var descriptor = props[i]; descriptor.enumerable = descriptor.enumerable || false; descriptor.configurable = true; if ("value" in descriptor) descriptor.writable = true; Object.defineProperty(target, descriptor.key, descriptor); } } return function (Constructor, protoProps, staticProps) { if (protoProps) defineProperties(Constructor.prototype, protoProps); if (staticProps) defineProperties(Constructor, staticProps); return Constructor; }; }();

  function _classCallCheck(instance, Constructor) { if (!(instance instanceof Constructor)) { throw new TypeError("Cannot call a class as a function"); } }

  /**
   * This work is licensed under the W3C Software and Document License
   * (http://www.w3.org/Consortium/Legal/2015/copyright-software-and-document).
   */

  (function () {
    // Return early if we're not running inside of the browser.
    if (typeof window === 'undefined' || typeof Element === 'undefined') {
      return;
    }

    // Convenience function for converting NodeLists.
    /** @type {typeof Array.prototype.slice} */
    var slice = Array.prototype.slice;

    /**
     * IE has a non-standard name for "matches".
     * @type {typeof Element.prototype.matches}
     */
    var matches = Element.prototype.matches || Element.prototype.msMatchesSelector;

    /** @type {string} */
    var _focusableElementsString = ['a[href]', 'area[href]', 'input:not([disabled])', 'select:not([disabled])', 'textarea:not([disabled])', 'button:not([disabled])', 'details', 'summary', 'iframe', 'object', 'embed', 'video', '[contenteditable]'].join(',');

    /**
     * `InertRoot` manages a single inert subtree, i.e. a DOM subtree whose root element has an `inert`
     * attribute.
     *
     * Its main functions are:
     *
     * - to create and maintain a set of managed `InertNode`s, including when mutations occur in the
     *   subtree. The `makeSubtreeUnfocusable()` method handles collecting `InertNode`s via registering
     *   each focusable node in the subtree with the singleton `InertManager` which manages all known
     *   focusable nodes within inert subtrees. `InertManager` ensures that a single `InertNode`
     *   instance exists for each focusable node which has at least one inert root as an ancestor.
     *
     * - to notify all managed `InertNode`s when this subtree stops being inert (i.e. when the `inert`
     *   attribute is removed from the root node). This is handled in the destructor, which calls the
     *   `deregister` method on `InertManager` for each managed inert node.
     */

    var InertRoot = function () {
      /**
       * @param {!HTMLElement} rootElement The HTMLElement at the root of the inert subtree.
       * @param {!InertManager} inertManager The global singleton InertManager object.
       */
      function InertRoot(rootElement, inertManager) {
        _classCallCheck(this, InertRoot);

        /** @type {!InertManager} */
        this._inertManager = inertManager;

        /** @type {!HTMLElement} */
        this._rootElement = rootElement;

        /**
         * @type {!Set<!InertNode>}
         * All managed focusable nodes in this InertRoot's subtree.
         */
        this._managedNodes = new Set();

        // Make the subtree hidden from assistive technology
        if (this._rootElement.hasAttribute('aria-hidden')) {
          /** @type {?string} */
          this._savedAriaHidden = this._rootElement.getAttribute('aria-hidden');
        } else {
          this._savedAriaHidden = null;
        }
        this._rootElement.setAttribute('aria-hidden', 'true');

        // Make all focusable elements in the subtree unfocusable and add them to _managedNodes
        this._makeSubtreeUnfocusable(this._rootElement);

        // Watch for:
        // - any additions in the subtree: make them unfocusable too
        // - any removals from the subtree: remove them from this inert root's managed nodes
        // - attribute changes: if `tabindex` is added, or removed from an intrinsically focusable
        //   element, make that node a managed node.
        this._observer = new MutationObserver(this._onMutation.bind(this));
        this._observer.observe(this._rootElement, { attributes: true, childList: true, subtree: true });
      }

      /**
       * Call this whenever this object is about to become obsolete.  This unwinds all of the state
       * stored in this object and updates the state of all of the managed nodes.
       */


      _createClass(InertRoot, [{
        key: 'destructor',
        value: function destructor() {
          this._observer.disconnect();

          if (this._rootElement) {
            if (this._savedAriaHidden !== null) {
              this._rootElement.setAttribute('aria-hidden', this._savedAriaHidden);
            } else {
              this._rootElement.removeAttribute('aria-hidden');
            }
          }

          this._managedNodes.forEach(function (inertNode) {
            this._unmanageNode(inertNode.node);
          }, this);

          // Note we cast the nulls to the ANY type here because:
          // 1) We want the class properties to be declared as non-null, or else we
          //    need even more casts throughout this code. All bets are off if an
          //    instance has been destroyed and a method is called.
          // 2) We don't want to cast "this", because we want type-aware optimizations
          //    to know which properties we're setting.
          this._observer = /** @type {?} */null;
          this._rootElement = /** @type {?} */null;
          this._managedNodes = /** @type {?} */null;
          this._inertManager = /** @type {?} */null;
        }

        /**
         * @return {!Set<!InertNode>} A copy of this InertRoot's managed nodes set.
         */

      }, {
        key: '_makeSubtreeUnfocusable',


        /**
         * @param {!Node} startNode
         */
        value: function _makeSubtreeUnfocusable(startNode) {
          var _this2 = this;

          composedTreeWalk(startNode, function (node) {
            return _this2._visitNode(node);
          });

          var activeElement = document.activeElement;

          if (!document.body.contains(startNode)) {
            // startNode may be in shadow DOM, so find its nearest shadowRoot to get the activeElement.
            var node = startNode;
            /** @type {!ShadowRoot|undefined} */
            var root = undefined;
            while (node) {
              if (node.nodeType === Node.DOCUMENT_FRAGMENT_NODE) {
                root = /** @type {!ShadowRoot} */node;
                break;
              }
              node = node.parentNode;
            }
            if (root) {
              activeElement = root.activeElement;
            }
          }
          if (startNode.contains(activeElement)) {
            activeElement.blur();
            // In IE11, if an element is already focused, and then set to tabindex=-1
            // calling blur() will not actually move the focus.
            // To work around this we call focus() on the body instead.
            if (activeElement === document.activeElement) {
              document.body.focus();
            }
          }
        }

        /**
         * @param {!Node} node
         */

      }, {
        key: '_visitNode',
        value: function _visitNode(node) {
          if (node.nodeType !== Node.ELEMENT_NODE) {
            return;
          }
          var element = /** @type {!HTMLElement} */node;

          // If a descendant inert root becomes un-inert, its descendants will still be inert because of
          // this inert root, so all of its managed nodes need to be adopted by this InertRoot.
          if (element !== this._rootElement && element.hasAttribute('inert')) {
            this._adoptInertRoot(element);
          }

          if (matches.call(element, _focusableElementsString) || element.hasAttribute('tabindex')) {
            this._manageNode(element);
          }
        }

        /**
         * Register the given node with this InertRoot and with InertManager.
         * @param {!Node} node
         */

      }, {
        key: '_manageNode',
        value: function _manageNode(node) {
          var inertNode = this._inertManager.register(node, this);
          this._managedNodes.add(inertNode);
        }

        /**
         * Unregister the given node with this InertRoot and with InertManager.
         * @param {!Node} node
         */

      }, {
        key: '_unmanageNode',
        value: function _unmanageNode(node) {
          var inertNode = this._inertManager.deregister(node, this);
          if (inertNode) {
            this._managedNodes['delete'](inertNode);
          }
        }

        /**
         * Unregister the entire subtree starting at `startNode`.
         * @param {!Node} startNode
         */

      }, {
        key: '_unmanageSubtree',
        value: function _unmanageSubtree(startNode) {
          var _this3 = this;

          composedTreeWalk(startNode, function (node) {
            return _this3._unmanageNode(node);
          });
        }

        /**
         * If a descendant node is found with an `inert` attribute, adopt its managed nodes.
         * @param {!HTMLElement} node
         */

      }, {
        key: '_adoptInertRoot',
        value: function _adoptInertRoot(node) {
          var inertSubroot = this._inertManager.getInertRoot(node);

          // During initialisation this inert root may not have been registered yet,
          // so register it now if need be.
          if (!inertSubroot) {
            this._inertManager.setInert(node, true);
            inertSubroot = this._inertManager.getInertRoot(node);
          }

          inertSubroot.managedNodes.forEach(function (savedInertNode) {
            this._manageNode(savedInertNode.node);
          }, this);
        }

        /**
         * Callback used when mutation observer detects subtree additions, removals, or attribute changes.
         * @param {!Array<!MutationRecord>} records
         * @param {!MutationObserver} self
         */

      }, {
        key: '_onMutation',
        value: function _onMutation(records, self) {
          records.forEach(function (record) {
            var target = /** @type {!HTMLElement} */record.target;
            if (record.type === 'childList') {
              // Manage added nodes
              slice.call(record.addedNodes).forEach(function (node) {
                this._makeSubtreeUnfocusable(node);
              }, this);

              // Un-manage removed nodes
              slice.call(record.removedNodes).forEach(function (node) {
                this._unmanageSubtree(node);
              }, this);
            } else if (record.type === 'attributes') {
              if (record.attributeName === 'tabindex') {
                // Re-initialise inert node if tabindex changes
                this._manageNode(target);
              } else if (target !== this._rootElement && record.attributeName === 'inert' && target.hasAttribute('inert')) {
                // If a new inert root is added, adopt its managed nodes and make sure it knows about the
                // already managed nodes from this inert subroot.
                this._adoptInertRoot(target);
                var inertSubroot = this._inertManager.getInertRoot(target);
                this._managedNodes.forEach(function (managedNode) {
                  if (target.contains(managedNode.node)) {
                    inertSubroot._manageNode(managedNode.node);
                  }
                });
              }
            }
          }, this);
        }
      }, {
        key: 'managedNodes',
        get: function get() {
          return new Set(this._managedNodes);
        }

        /** @return {boolean} */

      }, {
        key: 'hasSavedAriaHidden',
        get: function get() {
          return this._savedAriaHidden !== null;
        }

        /** @param {?string} ariaHidden */

      }, {
        key: 'savedAriaHidden',
        set: function set(ariaHidden) {
          this._savedAriaHidden = ariaHidden;
        }

        /** @return {?string} */
        ,
        get: function get() {
          return this._savedAriaHidden;
        }
      }]);

      return InertRoot;
    }();

    /**
     * `InertNode` initialises and manages a single inert node.
     * A node is inert if it is a descendant of one or more inert root elements.
     *
     * On construction, `InertNode` saves the existing `tabindex` value for the node, if any, and
     * either removes the `tabindex` attribute or sets it to `-1`, depending on whether the element
     * is intrinsically focusable or not.
     *
     * `InertNode` maintains a set of `InertRoot`s which are descendants of this `InertNode`. When an
     * `InertRoot` is destroyed, and calls `InertManager.deregister()`, the `InertManager` notifies the
     * `InertNode` via `removeInertRoot()`, which in turn destroys the `InertNode` if no `InertRoot`s
     * remain in the set. On destruction, `InertNode` reinstates the stored `tabindex` if one exists,
     * or removes the `tabindex` attribute if the element is intrinsically focusable.
     */


    var InertNode = function () {
      /**
       * @param {!Node} node A focusable element to be made inert.
       * @param {!InertRoot} inertRoot The inert root element associated with this inert node.
       */
      function InertNode(node, inertRoot) {
        _classCallCheck(this, InertNode);

        /** @type {!Node} */
        this._node = node;

        /** @type {boolean} */
        this._overrodeFocusMethod = false;

        /**
         * @type {!Set<!InertRoot>} The set of descendant inert roots.
         *    If and only if this set becomes empty, this node is no longer inert.
         */
        this._inertRoots = new Set([inertRoot]);

        /** @type {?number} */
        this._savedTabIndex = null;

        /** @type {boolean} */
        this._destroyed = false;

        // Save any prior tabindex info and make this node untabbable
        this.ensureUntabbable();
      }

      /**
       * Call this whenever this object is about to become obsolete.
       * This makes the managed node focusable again and deletes all of the previously stored state.
       */


      _createClass(InertNode, [{
        key: 'destructor',
        value: function destructor() {
          this._throwIfDestroyed();

          if (this._node && this._node.nodeType === Node.ELEMENT_NODE) {
            var element = /** @type {!HTMLElement} */this._node;
            if (this._savedTabIndex !== null) {
              element.setAttribute('tabindex', this._savedTabIndex);
            } else {
              element.removeAttribute('tabindex');
            }

            // Use `delete` to restore native focus method.
            if (this._overrodeFocusMethod) {
              delete element.focus;
            }
          }

          // See note in InertRoot.destructor for why we cast these nulls to ANY.
          this._node = /** @type {?} */null;
          this._inertRoots = /** @type {?} */null;
          this._destroyed = true;
        }

        /**
         * @type {boolean} Whether this object is obsolete because the managed node is no longer inert.
         * If the object has been destroyed, any attempt to access it will cause an exception.
         */

      }, {
        key: '_throwIfDestroyed',


        /**
         * Throw if user tries to access destroyed InertNode.
         */
        value: function _throwIfDestroyed() {
          if (this.destroyed) {
            throw new Error('Trying to access destroyed InertNode');
          }
        }

        /** @return {boolean} */

      }, {
        key: 'ensureUntabbable',


        /** Save the existing tabindex value and make the node untabbable and unfocusable */
        value: function ensureUntabbable() {
          if (this.node.nodeType !== Node.ELEMENT_NODE) {
            return;
          }
          var element = /** @type {!HTMLElement} */this.node;
          if (matches.call(element, _focusableElementsString)) {
            if ( /** @type {!HTMLElement} */element.tabIndex === -1 && this.hasSavedTabIndex) {
              return;
            }

            if (element.hasAttribute('tabindex')) {
              this._savedTabIndex = /** @type {!HTMLElement} */element.tabIndex;
            }
            element.setAttribute('tabindex', '-1');
            if (element.nodeType === Node.ELEMENT_NODE) {
              element.focus = function () {};
              this._overrodeFocusMethod = true;
            }
          } else if (element.hasAttribute('tabindex')) {
            this._savedTabIndex = /** @type {!HTMLElement} */element.tabIndex;
            element.removeAttribute('tabindex');
          }
        }

        /**
         * Add another inert root to this inert node's set of managing inert roots.
         * @param {!InertRoot} inertRoot
         */

      }, {
        key: 'addInertRoot',
        value: function addInertRoot(inertRoot) {
          this._throwIfDestroyed();
          this._inertRoots.add(inertRoot);
        }

        /**
         * Remove the given inert root from this inert node's set of managing inert roots.
         * If the set of managing inert roots becomes empty, this node is no longer inert,
         * so the object should be destroyed.
         * @param {!InertRoot} inertRoot
         */

      }, {
        key: 'removeInertRoot',
        value: function removeInertRoot(inertRoot) {
          this._throwIfDestroyed();
          this._inertRoots['delete'](inertRoot);
          if (this._inertRoots.size === 0) {
            this.destructor();
          }
        }
      }, {
        key: 'destroyed',
        get: function get() {
          return (/** @type {!InertNode} */this._destroyed
          );
        }
      }, {
        key: 'hasSavedTabIndex',
        get: function get() {
          return this._savedTabIndex !== null;
        }

        /** @return {!Node} */

      }, {
        key: 'node',
        get: function get() {
          this._throwIfDestroyed();
          return this._node;
        }

        /** @param {?number} tabIndex */

      }, {
        key: 'savedTabIndex',
        set: function set(tabIndex) {
          this._throwIfDestroyed();
          this._savedTabIndex = tabIndex;
        }

        /** @return {?number} */
        ,
        get: function get() {
          this._throwIfDestroyed();
          return this._savedTabIndex;
        }
      }]);

      return InertNode;
    }();

    /**
     * InertManager is a per-document singleton object which manages all inert roots and nodes.
     *
     * When an element becomes an inert root by having an `inert` attribute set and/or its `inert`
     * property set to `true`, the `setInert` method creates an `InertRoot` object for the element.
     * The `InertRoot` in turn registers itself as managing all of the element's focusable descendant
     * nodes via the `register()` method. The `InertManager` ensures that a single `InertNode` instance
     * is created for each such node, via the `_managedNodes` map.
     */


    var InertManager = function () {
      /**
       * @param {!Document} document
       */
      function InertManager(document) {
        _classCallCheck(this, InertManager);

        if (!document) {
          throw new Error('Missing required argument; InertManager needs to wrap a document.');
        }

        /** @type {!Document} */
        this._document = document;

        /**
         * All managed nodes known to this InertManager. In a map to allow looking up by Node.
         * @type {!Map<!Node, !InertNode>}
         */
        this._managedNodes = new Map();

        /**
         * All inert roots known to this InertManager. In a map to allow looking up by Node.
         * @type {!Map<!Node, !InertRoot>}
         */
        this._inertRoots = new Map();

        /**
         * Observer for mutations on `document.body`.
         * @type {!MutationObserver}
         */
        this._observer = new MutationObserver(this._watchForInert.bind(this));

        // Add inert style.
        addInertStyle(document.head || document.body || document.documentElement);

        // Wait for document to be loaded.
        if (document.readyState === 'loading') {
          document.addEventListener('DOMContentLoaded', this._onDocumentLoaded.bind(this));
        } else {
          this._onDocumentLoaded();
        }
      }

      /**
       * Set whether the given element should be an inert root or not.
       * @param {!HTMLElement} root
       * @param {boolean} inert
       */


      _createClass(InertManager, [{
        key: 'setInert',
        value: function setInert(root, inert) {
          if (inert) {
            if (this._inertRoots.has(root)) {
              // element is already inert
              return;
            }

            var inertRoot = new InertRoot(root, this);
            root.setAttribute('inert', '');
            this._inertRoots.set(root, inertRoot);
            // If not contained in the document, it must be in a shadowRoot.
            // Ensure inert styles are added there.
            if (!this._document.body.contains(root)) {
              var parent = root.parentNode;
              while (parent) {
                if (parent.nodeType === 11) {
                  addInertStyle(parent);
                }
                parent = parent.parentNode;
              }
            }
          } else {
            if (!this._inertRoots.has(root)) {
              // element is already non-inert
              return;
            }

            var _inertRoot = this._inertRoots.get(root);
            _inertRoot.destructor();
            this._inertRoots['delete'](root);
            root.removeAttribute('inert');
          }
        }

        /**
         * Get the InertRoot object corresponding to the given inert root element, if any.
         * @param {!Node} element
         * @return {!InertRoot|undefined}
         */

      }, {
        key: 'getInertRoot',
        value: function getInertRoot(element) {
          return this._inertRoots.get(element);
        }

        /**
         * Register the given InertRoot as managing the given node.
         * In the case where the node has a previously existing inert root, this inert root will
         * be added to its set of inert roots.
         * @param {!Node} node
         * @param {!InertRoot} inertRoot
         * @return {!InertNode} inertNode
         */

      }, {
        key: 'register',
        value: function register(node, inertRoot) {
          var inertNode = this._managedNodes.get(node);
          if (inertNode !== undefined) {
            // node was already in an inert subtree
            inertNode.addInertRoot(inertRoot);
          } else {
            inertNode = new InertNode(node, inertRoot);
          }

          this._managedNodes.set(node, inertNode);

          return inertNode;
        }

        /**
         * De-register the given InertRoot as managing the given inert node.
         * Removes the inert root from the InertNode's set of managing inert roots, and remove the inert
         * node from the InertManager's set of managed nodes if it is destroyed.
         * If the node is not currently managed, this is essentially a no-op.
         * @param {!Node} node
         * @param {!InertRoot} inertRoot
         * @return {?InertNode} The potentially destroyed InertNode associated with this node, if any.
         */

      }, {
        key: 'deregister',
        value: function deregister(node, inertRoot) {
          var inertNode = this._managedNodes.get(node);
          if (!inertNode) {
            return null;
          }

          inertNode.removeInertRoot(inertRoot);
          if (inertNode.destroyed) {
            this._managedNodes['delete'](node);
          }

          return inertNode;
        }

        /**
         * Callback used when document has finished loading.
         */

      }, {
        key: '_onDocumentLoaded',
        value: function _onDocumentLoaded() {
          // Find all inert roots in document and make them actually inert.
          var inertElements = slice.call(this._document.querySelectorAll('[inert]'));
          inertElements.forEach(function (inertElement) {
            this.setInert(inertElement, true);
          }, this);

          // Comment this out to use programmatic API only.
          this._observer.observe(this._document.body || this._document.documentElement, { attributes: true, subtree: true, childList: true });
        }

        /**
         * Callback used when mutation observer detects attribute changes.
         * @param {!Array<!MutationRecord>} records
         * @param {!MutationObserver} self
         */

      }, {
        key: '_watchForInert',
        value: function _watchForInert(records, self) {
          var _this = this;
          records.forEach(function (record) {
            switch (record.type) {
              case 'childList':
                slice.call(record.addedNodes).forEach(function (node) {
                  if (node.nodeType !== Node.ELEMENT_NODE) {
                    return;
                  }
                  var inertElements = slice.call(node.querySelectorAll('[inert]'));
                  if (matches.call(node, '[inert]')) {
                    inertElements.unshift(node);
                  }
                  inertElements.forEach(function (inertElement) {
                    this.setInert(inertElement, true);
                  }, _this);
                }, _this);
                break;
              case 'attributes':
                if (record.attributeName !== 'inert') {
                  return;
                }
                var target = /** @type {!HTMLElement} */record.target;
                var inert = target.hasAttribute('inert');
                _this.setInert(target, inert);
                break;
            }
          }, this);
        }
      }]);

      return InertManager;
    }();

    /**
     * Recursively walk the composed tree from |node|.
     * @param {!Node} node
     * @param {(function (!HTMLElement))=} callback Callback to be called for each element traversed,
     *     before descending into child nodes.
     * @param {?ShadowRoot=} shadowRootAncestor The nearest ShadowRoot ancestor, if any.
     */


    function composedTreeWalk(node, callback, shadowRootAncestor) {
      if (node.nodeType == Node.ELEMENT_NODE) {
        var element = /** @type {!HTMLElement} */node;
        if (callback) {
          callback(element);
        }

        // Descend into node:
        // If it has a ShadowRoot, ignore all child elements - these will be picked
        // up by the <content> or <shadow> elements. Descend straight into the
        // ShadowRoot.
        var shadowRoot = /** @type {!HTMLElement} */element.shadowRoot;
        if (shadowRoot) {
          composedTreeWalk(shadowRoot, callback, shadowRoot);
          return;
        }

        // If it is a <content> element, descend into distributed elements - these
        // are elements from outside the shadow root which are rendered inside the
        // shadow DOM.
        if (element.localName == 'content') {
          var content = /** @type {!HTMLContentElement} */element;
          // Verifies if ShadowDom v0 is supported.
          var distributedNodes = content.getDistributedNodes ? content.getDistributedNodes() : [];
          for (var i = 0; i < distributedNodes.length; i++) {
            composedTreeWalk(distributedNodes[i], callback, shadowRootAncestor);
          }
          return;
        }

        // If it is a <slot> element, descend into assigned nodes - these
        // are elements from outside the shadow root which are rendered inside the
        // shadow DOM.
        if (element.localName == 'slot') {
          var slot = /** @type {!HTMLSlotElement} */element;
          // Verify if ShadowDom v1 is supported.
          var _distributedNodes = slot.assignedNodes ? slot.assignedNodes({ flatten: true }) : [];
          for (var _i = 0; _i < _distributedNodes.length; _i++) {
            composedTreeWalk(_distributedNodes[_i], callback, shadowRootAncestor);
          }
          return;
        }
      }

      // If it is neither the parent of a ShadowRoot, a <content> element, a <slot>
      // element, nor a <shadow> element recurse normally.
      var child = node.firstChild;
      while (child != null) {
        composedTreeWalk(child, callback, shadowRootAncestor);
        child = child.nextSibling;
      }
    }

    /**
     * Adds a style element to the node containing the inert specific styles
     * @param {!Node} node
     */
    function addInertStyle(node) {
      if (node.querySelector('style#inert-style, link#inert-style')) {
        return;
      }
      var style = document.createElement('style');
      style.setAttribute('id', 'inert-style');
      style.textContent = '\n' + '[inert] {\n' + '  pointer-events: none;\n' + '  cursor: default;\n' + '}\n' + '\n' + '[inert], [inert] * {\n' + '  -webkit-user-select: none;\n' + '  -moz-user-select: none;\n' + '  -ms-user-select: none;\n' + '  user-select: none;\n' + '}\n';
      node.appendChild(style);
    }

    if (!HTMLElement.prototype.hasOwnProperty('inert')) {
      /** @type {!InertManager} */
      var inertManager = new InertManager(document);

      Object.defineProperty(HTMLElement.prototype, 'inert', {
        enumerable: true,
        /** @this {!HTMLElement} */
        get: function get() {
          return this.hasAttribute('inert');
        },
        /** @this {!HTMLElement} */
        set: function set(inert) {
          inertManager.setInert(this, inert);
        }
      });
    }
  })();

})));