Version 3.18.1
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File: event/js/event-dom.js

            (function() {
            
            /**
             * The event utility provides functions to add and remove event listeners,
             * event cleansing.  It also tries to automatically remove listeners it
             * registers during the unload event.
             * @module event
             * @main event
             * @submodule event-base
             */
            
            /**
             * The event utility provides functions to add and remove event listeners,
             * event cleansing.  It also tries to automatically remove listeners it
             * registers during the unload event.
             *
             * @class Event
             * @static
             */
            
            Y.Env.evt.dom_wrappers = {};
            Y.Env.evt.dom_map = {};
            
            var _eventenv = Y.Env.evt,
                config = Y.config,
                win = config.win,
                add = YUI.Env.add,
                remove = YUI.Env.remove,
            
                onLoad = function() {
                    YUI.Env.windowLoaded = true;
                    Y.Event._load();
                    remove(win, "load", onLoad);
                },
            
                onUnload = function() {
                    Y.Event._unload();
                },
            
                EVENT_READY = 'domready',
            
                COMPAT_ARG = '~yui|2|compat~',
            
                shouldIterate = function(o) {
                    try {
                        // TODO: See if there's a more performant way to return true early on this, for the common case
                        return (o && typeof o !== "string" && Y.Lang.isNumber(o.length) && !o.tagName && !Y.DOM.isWindow(o));
                    } catch(ex) {
                        Y.log("collection check failure", "warn", "event");
                        return false;
                    }
                },
            
                // aliases to support DOM event subscription clean up when the last
                // subscriber is detached. deleteAndClean overrides the DOM event's wrapper
                // CustomEvent _delete method.
                _ceProtoDelete = Y.CustomEvent.prototype._delete,
                _deleteAndClean = function(s) {
                    var ret = _ceProtoDelete.apply(this, arguments);
            
                    if (!this.hasSubs()) {
                        Y.Event._clean(this);
                    }
            
                    return ret;
                },
            
            Event = function() {
            
                /**
                 * True after the onload event has fired
                 * @property _loadComplete
                 * @type boolean
                 * @static
                 * @private
                 */
                var _loadComplete =  false,
            
                /**
                 * The number of times to poll after window.onload.  This number is
                 * increased if additional late-bound handlers are requested after
                 * the page load.
                 * @property _retryCount
                 * @static
                 * @private
                 */
                _retryCount = 0,
            
                /**
                 * onAvailable listeners
                 * @property _avail
                 * @static
                 * @private
                 */
                _avail = [],
            
                /**
                 * Custom event wrappers for DOM events.  Key is
                 * 'event:' + Element uid stamp + event type
                 * @property _wrappers
                 * @type CustomEvent
                 * @static
                 * @private
                 */
                _wrappers = _eventenv.dom_wrappers,
            
                _windowLoadKey = null,
            
                /**
                 * Custom event wrapper map DOM events.  Key is
                 * Element uid stamp.  Each item is a hash of custom event
                 * wrappers as provided in the _wrappers collection.  This
                 * provides the infrastructure for getListeners.
                 * @property _el_events
                 * @static
                 * @private
                 */
                _el_events = _eventenv.dom_map;
            
                return {
            
                    /**
                     * The number of times we should look for elements that are not
                     * in the DOM at the time the event is requested after the document
                     * has been loaded.  The default is 1000@amp;40 ms, so it will poll
                     * for 40 seconds or until all outstanding handlers are bound
                     * (whichever comes first).
                     * @property POLL_RETRYS
                     * @type int
                     * @static
                     * @final
                     */
                    POLL_RETRYS: 1000,
            
                    /**
                     * The poll interval in milliseconds
                     * @property POLL_INTERVAL
                     * @type int
                     * @static
                     * @final
                     */
                    POLL_INTERVAL: 40,
            
                    /**
                     * addListener/removeListener can throw errors in unexpected scenarios.
                     * These errors are suppressed, the method returns false, and this property
                     * is set
                     * @property lastError
                     * @static
                     * @type Error
                     */
                    lastError: null,
            
            
                    /**
                     * poll handle
                     * @property _interval
                     * @static
                     * @private
                     */
                    _interval: null,
            
                    /**
                     * document readystate poll handle
                     * @property _dri
                     * @static
                     * @private
                     */
                     _dri: null,
            
                    /**
                     * True when the document is initially usable
                     * @property DOMReady
                     * @type boolean
                     * @static
                     */
                    DOMReady: false,
            
                    /**
                     * @method startInterval
                     * @static
                     * @private
                     */
                    startInterval: function() {
                        if (!Event._interval) {
            Event._interval = setInterval(Event._poll, Event.POLL_INTERVAL);
                        }
                    },
            
                    /**
                     * Executes the supplied callback when the item with the supplied
                     * id is found.  This is meant to be used to execute behavior as
                     * soon as possible as the page loads.  If you use this after the
                     * initial page load it will poll for a fixed time for the element.
                     * The number of times it will poll and the frequency are
                     * configurable.  By default it will poll for 10 seconds.
                     *
                     * <p>The callback is executed with a single parameter:
                     * the custom object parameter, if provided.</p>
                     *
                     * @method onAvailable
                     *
                     * @param {string||string[]}   id the id of the element, or an array
                     * of ids to look for.
                     * @param {function} fn what to execute when the element is found.
                     * @param {object}   p_obj an optional object to be passed back as
                     *                   a parameter to fn.
                     * @param {boolean|object}  p_override If set to true, fn will execute
                     *                   in the context of p_obj, if set to an object it
                     *                   will execute in the context of that object
                     * @param checkContent {boolean} check child node readiness (onContentReady)
                     * @static
                     * @deprecated Use Y.on("available")
                     */
                    // @TODO fix arguments
                    onAvailable: function(id, fn, p_obj, p_override, checkContent, compat) {
            
                        var a = Y.Array(id), i, availHandle;
            
                        for (i=0; i<a.length; i=i+1) {
                            _avail.push({
                                id:         a[i],
                                fn:         fn,
                                obj:        p_obj,
                                override:   p_override,
                                checkReady: checkContent,
                                compat:     compat
                            });
                        }
                        _retryCount = this.POLL_RETRYS;
            
                        // We want the first test to be immediate, but async
                        setTimeout(Event._poll, 0);
            
                        availHandle = new Y.EventHandle({
            
                            _delete: function() {
                                // set by the event system for lazy DOM listeners
                                if (availHandle.handle) {
                                    availHandle.handle.detach();
                                    return;
                                }
            
                                var i, j;
            
                                // otherwise try to remove the onAvailable listener(s)
                                for (i = 0; i < a.length; i++) {
                                    for (j = 0; j < _avail.length; j++) {
                                        if (a[i] === _avail[j].id) {
                                            _avail.splice(j, 1);
                                        }
                                    }
                                }
                            }
            
                        });
            
                        return availHandle;
                    },
            
                    /**
                     * Works the same way as onAvailable, but additionally checks the
                     * state of sibling elements to determine if the content of the
                     * available element is safe to modify.
                     *
                     * <p>The callback is executed with a single parameter:
                     * the custom object parameter, if provided.</p>
                     *
                     * @method onContentReady
                     *
                     * @param {string}   id the id of the element to look for.
                     * @param {function} fn what to execute when the element is ready.
                     * @param {object}   obj an optional object to be passed back as
                     *                   a parameter to fn.
                     * @param {boolean|object}  override If set to true, fn will execute
                     *                   in the context of p_obj.  If an object, fn will
                     *                   exectute in the context of that object
                     *
                     * @static
                     * @deprecated Use Y.on("contentready")
                     */
                    // @TODO fix arguments
                    onContentReady: function(id, fn, obj, override, compat) {
                        return Event.onAvailable(id, fn, obj, override, true, compat);
                    },
            
                    /**
                     * Adds an event listener
                     *
                     * @method attach
                     *
                     * @param {String}   type     The type of event to append
                     * @param {Function} fn        The method the event invokes
                     * @param {String|HTMLElement|Array|NodeList} el An id, an element
                     *  reference, or a collection of ids and/or elements to assign the
                     *  listener to.
                     * @param {Object}   context optional context object
                     * @param {Boolean|object}  args 0..n arguments to pass to the callback
                     * @return {EventHandle} an object to that can be used to detach the listener
                     *
                     * @static
                     */
            
                    attach: function(type, fn, el, context) {
                        return Event._attach(Y.Array(arguments, 0, true));
                    },
            
                    _createWrapper: function (el, type, capture, compat, facade) {
            
                        var cewrapper,
                            ek  = Y.stamp(el),
                            key = 'event:' + ek + type;
            
                        if (false === facade) {
                            key += 'native';
                        }
                        if (capture) {
                            key += 'capture';
                        }
            
            
                        cewrapper = _wrappers[key];
            
            
                        if (!cewrapper) {
                            // create CE wrapper
                            cewrapper = Y.publish(key, {
                                silent: true,
                                bubbles: false,
                                emitFacade:false,
                                contextFn: function() {
                                    if (compat) {
                                        return cewrapper.el;
                                    } else {
                                        cewrapper.nodeRef = cewrapper.nodeRef || Y.one(cewrapper.el);
                                        return cewrapper.nodeRef;
                                    }
                                }
                            });
            
                            cewrapper.overrides = {};
            
                            // for later removeListener calls
                            cewrapper.el = el;
                            cewrapper.key = key;
                            cewrapper.domkey = ek;
                            cewrapper.type = type;
                            cewrapper.fn = function(e) {
                                cewrapper.fire(Event.getEvent(e, el, (compat || (false === facade))));
                            };
                            cewrapper.capture = capture;
            
                            if (el == win && type == "load") {
                                // window load happens once
                                cewrapper.fireOnce = true;
                                _windowLoadKey = key;
                            }
                            cewrapper._delete = _deleteAndClean;
            
                            _wrappers[key] = cewrapper;
                            _el_events[ek] = _el_events[ek] || {};
                            _el_events[ek][key] = cewrapper;
            
                            add(el, type, cewrapper.fn, capture);
                        }
            
                        return cewrapper;
            
                    },
            
                    _attach: function(args, conf) {
            
                        var compat,
                            handles, oEl, cewrapper, context,
                            fireNow = false, ret,
                            type = args[0],
                            fn = args[1],
                            el = args[2] || win,
                            facade = conf && conf.facade,
                            capture = conf && conf.capture,
                            overrides = conf && conf.overrides;
            
                        if (args[args.length-1] === COMPAT_ARG) {
                            compat = true;
                        }
            
                        if (!fn || !fn.call) {
                            Y.log(type + " attach call failed, invalid callback", "error", "event");
                            return false;
                        }
            
                        // The el argument can be an array of elements or element ids.
                        if (shouldIterate(el)) {
            
                            handles=[];
            
                            Y.each(el, function(v, k) {
                                args[2] = v;
                                handles.push(Event._attach(args.slice(), conf));
                            });
            
                            // return (handles.length === 1) ? handles[0] : handles;
                            return new Y.EventHandle(handles);
            
                        // If the el argument is a string, we assume it is
                        // actually the id of the element.  If the page is loaded
                        // we convert el to the actual element, otherwise we
                        // defer attaching the event until the element is
                        // ready
                        } else if (Y.Lang.isString(el)) {
            
                            // oEl = (compat) ? Y.DOM.byId(el) : Y.Selector.query(el);
            
                            if (compat) {
                                oEl = Y.DOM.byId(el);
                            } else {
            
                                oEl = Y.Selector.query(el);
            
                                switch (oEl.length) {
                                    case 0:
                                        oEl = null;
                                        break;
                                    case 1:
                                        oEl = oEl[0];
                                        break;
                                    default:
                                        args[2] = oEl;
                                        return Event._attach(args, conf);
                                }
                            }
            
                            if (oEl) {
            
                                el = oEl;
            
                            // Not found = defer adding the event until the element is available
                            } else {
            
                                ret = Event.onAvailable(el, function() {
            
                                    ret.handle = Event._attach(args, conf);
            
                                }, Event, true, false, compat);
            
                                return ret;
            
                            }
                        }
            
                        // Element should be an html element or node
                        if (!el) {
                            Y.log("unable to attach event " + type, "warn", "event");
                            return false;
                        }
            
                        if (Y.Node && Y.instanceOf(el, Y.Node)) {
                            el = Y.Node.getDOMNode(el);
                        }
            
                        cewrapper = Event._createWrapper(el, type, capture, compat, facade);
                        if (overrides) {
                            Y.mix(cewrapper.overrides, overrides);
                        }
            
                        if (el == win && type == "load") {
            
                            // if the load is complete, fire immediately.
                            // all subscribers, including the current one
                            // will be notified.
                            if (YUI.Env.windowLoaded) {
                                fireNow = true;
                            }
                        }
            
                        if (compat) {
                            args.pop();
                        }
            
                        context = args[3];
            
                        // set context to the Node if not specified
                        // ret = cewrapper.on.apply(cewrapper, trimmedArgs);
                        ret = cewrapper._on(fn, context, (args.length > 4) ? args.slice(4) : null);
            
                        if (fireNow) {
                            cewrapper.fire();
                        }
            
                        return ret;
            
                    },
            
                    /**
                     * Removes an event listener.  Supports the signature the event was bound
                     * with, but the preferred way to remove listeners is using the handle
                     * that is returned when using Y.on
                     *
                     * @method detach
                     *
                     * @param {String} type the type of event to remove.
                     * @param {Function} fn the method the event invokes.  If fn is
                     * undefined, then all event handlers for the type of event are
                     * removed.
                     * @param {String|HTMLElement|Array|NodeList|EventHandle} el An
                     * event handle, an id, an element reference, or a collection
                     * of ids and/or elements to remove the listener from.
                     * @return {boolean} true if the unbind was successful, false otherwise.
                     * @static
                     */
                    detach: function(type, fn, el, obj) {
            
                        var args=Y.Array(arguments, 0, true), compat, l, ok, i,
                            id, ce;
            
                        if (args[args.length-1] === COMPAT_ARG) {
                            compat = true;
                            // args.pop();
                        }
            
                        if (type && type.detach) {
                            return type.detach();
                        }
            
                        // The el argument can be a string
                        if (typeof el == "string") {
            
                            // el = (compat) ? Y.DOM.byId(el) : Y.all(el);
                            if (compat) {
                                el = Y.DOM.byId(el);
                            } else {
                                el = Y.Selector.query(el);
                                l = el.length;
                                if (l < 1) {
                                    el = null;
                                } else if (l == 1) {
                                    el = el[0];
                                }
                            }
                            // return Event.detach.apply(Event, args);
                        }
            
                        if (!el) {
                            return false;
                        }
            
                        if (el.detach) {
                            args.splice(2, 1);
                            return el.detach.apply(el, args);
                        // The el argument can be an array of elements or element ids.
                        } else if (shouldIterate(el)) {
                            ok = true;
                            for (i=0, l=el.length; i<l; ++i) {
                                args[2] = el[i];
                                ok = ( Y.Event.detach.apply(Y.Event, args) && ok );
                            }
            
                            return ok;
                        }
            
                        if (!type || !fn || !fn.call) {
                            return Event.purgeElement(el, false, type);
                        }
            
                        id = 'event:' + Y.stamp(el) + type;
                        ce = _wrappers[id];
            
                        if (ce) {
                            return ce.detach(fn);
                        } else {
                            return false;
                        }
            
                    },
            
                    /**
                     * Finds the event in the window object, the caller's arguments, or
                     * in the arguments of another method in the callstack.  This is
                     * executed automatically for events registered through the event
                     * manager, so the implementer should not normally need to execute
                     * this function at all.
                     * @method getEvent
                     * @param {Event} e the event parameter from the handler
                     * @param {HTMLElement} el the element the listener was attached to
                     * @return {Event} the event
                     * @static
                     */
                    getEvent: function(e, el, noFacade) {
                        var ev = e || win.event;
            
                        return (noFacade) ? ev :
                            new Y.DOMEventFacade(ev, el, _wrappers['event:' + Y.stamp(el) + e.type]);
                    },
            
                    /**
                     * Generates an unique ID for the element if it does not already
                     * have one.
                     * @method generateId
                     * @param el the element to create the id for
                     * @return {string} the resulting id of the element
                     * @static
                     */
                    generateId: function(el) {
                        return Y.DOM.generateID(el);
                    },
            
                    /**
                     * We want to be able to use getElementsByTagName as a collection
                     * to attach a group of events to.  Unfortunately, different
                     * browsers return different types of collections.  This function
                     * tests to determine if the object is array-like.  It will also
                     * fail if the object is an array, but is empty.
                     * @method _isValidCollection
                     * @param o the object to test
                     * @return {boolean} true if the object is array-like and populated
                     * @deprecated was not meant to be used directly
                     * @static
                     * @private
                     */
                    _isValidCollection: shouldIterate,
            
                    /**
                     * hook up any deferred listeners
                     * @method _load
                     * @static
                     * @private
                     */
                    _load: function(e) {
                        if (!_loadComplete) {
                            _loadComplete = true;
            
                            // Just in case DOMReady did not go off for some reason
                            // E._ready();
                            if (Y.fire) {
                                Y.fire(EVENT_READY);
                            }
            
                            // Available elements may not have been detected before the
                            // window load event fires. Try to find them now so that the
                            // the user is more likely to get the onAvailable notifications
                            // before the window load notification
                            Event._poll();
                        }
                    },
            
                    /**
                     * Polling function that runs before the onload event fires,
                     * attempting to attach to DOM Nodes as soon as they are
                     * available
                     * @method _poll
                     * @static
                     * @private
                     */
                    _poll: function() {
                        if (Event.locked) {
                            return;
                        }
            
                        if (Y.UA.ie && !YUI.Env.DOMReady) {
                            // Hold off if DOMReady has not fired and check current
                            // readyState to protect against the IE operation aborted
                            // issue.
                            Event.startInterval();
                            return;
                        }
            
                        Event.locked = true;
            
                        // keep trying until after the page is loaded.  We need to
                        // check the page load state prior to trying to bind the
                        // elements so that we can be certain all elements have been
                        // tested appropriately
                        var i, len, item, el, notAvail, executeItem,
                            tryAgain = !_loadComplete;
            
                        if (!tryAgain) {
                            tryAgain = (_retryCount > 0);
                        }
            
                        // onAvailable
                        notAvail = [];
            
                        executeItem = function (el, item) {
                            var context, ov = item.override;
                            try {
                                if (item.compat) {
                                    if (item.override) {
                                        if (ov === true) {
                                            context = item.obj;
                                        } else {
                                            context = ov;
                                        }
                                    } else {
                                        context = el;
                                    }
                                    item.fn.call(context, item.obj);
                                } else {
                                    context = item.obj || Y.one(el);
                                    item.fn.apply(context, (Y.Lang.isArray(ov)) ? ov : []);
                                }
                            } catch (e) {
                                Y.log("Error in available or contentReady callback", 'error', 'event');
                            }
                        };
            
                        // onAvailable
                        for (i=0,len=_avail.length; i<len; ++i) {
                            item = _avail[i];
                            if (item && !item.checkReady) {
            
                                // el = (item.compat) ? Y.DOM.byId(item.id) : Y.one(item.id);
                                el = (item.compat) ? Y.DOM.byId(item.id) : Y.Selector.query(item.id, null, true);
            
                                if (el) {
                                    executeItem(el, item);
                                    _avail[i] = null;
                                } else {
                                    notAvail.push(item);
                                }
                            }
                        }
            
                        // onContentReady
                        for (i=0,len=_avail.length; i<len; ++i) {
                            item = _avail[i];
                            if (item && item.checkReady) {
            
                                // el = (item.compat) ? Y.DOM.byId(item.id) : Y.one(item.id);
                                el = (item.compat) ? Y.DOM.byId(item.id) : Y.Selector.query(item.id, null, true);
            
                                if (el) {
                                    // The element is available, but not necessarily ready
                                    // @todo should we test parentNode.nextSibling?
                                    if (_loadComplete || (el.get && el.get('nextSibling')) || el.nextSibling) {
                                        executeItem(el, item);
                                        _avail[i] = null;
                                    }
                                } else {
                                    notAvail.push(item);
                                }
                            }
                        }
            
                        _retryCount = (notAvail.length === 0) ? 0 : _retryCount - 1;
            
                        if (tryAgain) {
                            // we may need to strip the nulled out items here
                            Event.startInterval();
                        } else {
                            clearInterval(Event._interval);
                            Event._interval = null;
                        }
            
                        Event.locked = false;
            
                        return;
            
                    },
            
                    /**
                     * Removes all listeners attached to the given element via addListener.
                     * Optionally, the node's children can also be purged.
                     * Optionally, you can specify a specific type of event to remove.
                     * @method purgeElement
                     * @param {HTMLElement} el the element to purge
                     * @param {boolean} recurse recursively purge this element's children
                     * as well.  Use with caution.
                     * @param {string} type optional type of listener to purge. If
                     * left out, all listeners will be removed
                     * @static
                     */
                    purgeElement: function(el, recurse, type) {
                        // var oEl = (Y.Lang.isString(el)) ? Y.one(el) : el,
                        var oEl = (Y.Lang.isString(el)) ?  Y.Selector.query(el, null, true) : el,
                            lis = Event.getListeners(oEl, type), i, len, children, child;
            
                        if (recurse && oEl) {
                            lis = lis || [];
                            children = Y.Selector.query('*', oEl);
                            len = children.length;
                            for (i = 0; i < len; ++i) {
                                child = Event.getListeners(children[i], type);
                                if (child) {
                                    lis = lis.concat(child);
                                }
                            }
                        }
            
                        if (lis) {
                            for (i = 0, len = lis.length; i < len; ++i) {
                                lis[i].detachAll();
                            }
                        }
            
                    },
            
                    /**
                     * Removes all object references and the DOM proxy subscription for
                     * a given event for a DOM node.
                     *
                     * @method _clean
                     * @param wrapper {CustomEvent} Custom event proxy for the DOM
                     *                  subscription
                     * @private
                     * @static
                     * @since 3.4.0
                     */
                    _clean: function (wrapper) {
                        var key    = wrapper.key,
                            domkey = wrapper.domkey;
            
                        remove(wrapper.el, wrapper.type, wrapper.fn, wrapper.capture);
                        delete _wrappers[key];
                        delete Y._yuievt.events[key];
                        if (_el_events[domkey]) {
                            delete _el_events[domkey][key];
                            if (!Y.Object.size(_el_events[domkey])) {
                                delete _el_events[domkey];
                            }
                        }
                    },
            
                    /**
                     * Returns all listeners attached to the given element via addListener.
                     * Optionally, you can specify a specific type of event to return.
                     * @method getListeners
                     * @param el {HTMLElement|string} the element or element id to inspect
                     * @param type {string} optional type of listener to return. If
                     * left out, all listeners will be returned
                     * @return {CustomEvent} the custom event wrapper for the DOM event(s)
                     * @static
                     */
                    getListeners: function(el, type) {
                        var ek = Y.stamp(el, true), evts = _el_events[ek],
                            results=[] , key = (type) ? 'event:' + ek + type : null,
                            adapters = _eventenv.plugins;
            
                        if (!evts) {
                            return null;
                        }
            
                        if (key) {
                            // look for synthetic events
                            if (adapters[type] && adapters[type].eventDef) {
                                key += '_synth';
                            }
            
                            if (evts[key]) {
                                results.push(evts[key]);
                            }
            
                            // get native events as well
                            key += 'native';
                            if (evts[key]) {
                                results.push(evts[key]);
                            }
            
                        } else {
                            Y.each(evts, function(v, k) {
                                results.push(v);
                            });
                        }
            
                        return (results.length) ? results : null;
                    },
            
                    /**
                     * Removes all listeners registered by pe.event.  Called
                     * automatically during the unload event.
                     * @method _unload
                     * @static
                     * @private
                     */
                    _unload: function(e) {
                        Y.each(_wrappers, function(v, k) {
                            if (v.type == 'unload') {
                                v.fire(e);
                            }
                            v.detachAll();
                        });
                        remove(win, "unload", onUnload);
                    },
            
                    /**
                     * Adds a DOM event directly without the caching, cleanup, context adj, etc
                     *
                     * @method nativeAdd
                     * @param {HTMLElement} el      the element to bind the handler to
                     * @param {string}      type   the type of event handler
                     * @param {function}    fn      the callback to invoke
                     * @param {Boolean}      capture capture or bubble phase
                     * @static
                     * @private
                     */
                    nativeAdd: add,
            
                    /**
                     * Basic remove listener
                     *
                     * @method nativeRemove
                     * @param {HTMLElement} el      the element to bind the handler to
                     * @param {string}      type   the type of event handler
                     * @param {function}    fn      the callback to invoke
                     * @param {Boolean}      capture capture or bubble phase
                     * @static
                     * @private
                     */
                    nativeRemove: remove
                };
            
            }();
            
            Y.Event = Event;
            
            if (config.injected || YUI.Env.windowLoaded) {
                onLoad();
            } else {
                add(win, "load", onLoad);
            }
            
            // Process onAvailable/onContentReady items when when the DOM is ready in IE
            if (Y.UA.ie) {
                Y.on(EVENT_READY, Event._poll);
            
                // In IE6 and below, detach event handlers when the page is unloaded in
                // order to try and prevent cross-page memory leaks. This isn't done in
                // other browsers because a) it's not necessary, and b) it breaks the
                // back/forward cache.
                if (Y.UA.ie < 7) {
                    try {
                        add(win, "unload", onUnload);
                    } catch(e) {
                        Y.log("Registering unload listener failed.", "warn", "event-base");
                    }
                }
            }
            
            Event.Custom = Y.CustomEvent;
            Event.Subscriber = Y.Subscriber;
            Event.Target = Y.EventTarget;
            Event.Handle = Y.EventHandle;
            Event.Facade = Y.EventFacade;
            
            Event._poll();
            
            }());