The source code

    /**
     * @class Ext.menu.Item
     * @extends Ext.menu.BaseItem
     * A base class for all menu items that require menu-related functionality (like sub-menus) and are not static
     * display items.  Item extends the base functionality of {@link Ext.menu.BaseItem} by adding menu-specific
     * activation and click handling.
     * @constructor
     * Creates a new Item
     * @param {Object} config Configuration options
     * @xtype menuitem
     */
    Ext.menu.Item = function(config){
        Ext.menu.Item.superclass.constructor.call(this, config);
        if(this.menu){
            this.menu = Ext.menu.MenuMgr.get(this.menu);
        }
    };
    Ext.extend(Ext.menu.Item, Ext.menu.BaseItem, {
        /**
         * @property menu
         * @type Ext.menu.Menu
         * The submenu associated with this Item if one was configured.
         */
        /**
         * @cfg {Mixed} menu (optional) Either an instance of {@link Ext.menu.Menu} or the config object for an
         * {@link Ext.menu.Menu} which acts as the submenu when this item is activated.
         */
        /**
         * @cfg {String} icon The path to an icon to display in this item (defaults to Ext.BLANK_IMAGE_URL).  If
         * icon is specified {@link #iconCls} should not be.
         */
        /**
         * @cfg {String} iconCls A CSS class that specifies a background image that will be used as the icon for
         * this item (defaults to '').  If iconCls is specified {@link #icon} should not be.
         */
        /**
         * @cfg {String} text The text to display in this item (defaults to '').
         */
        /**
         * @cfg {String} href The href attribute to use for the underlying anchor link (defaults to '#').
         */
        /**
         * @cfg {String} hrefTarget The target attribute to use for the underlying anchor link (defaults to '').
         */
        /**
         * @cfg {String} itemCls The default CSS class to use for menu items (defaults to 'x-menu-item')
         */
        itemCls : 'x-menu-item',
        /**
         * @cfg {Boolean} canActivate True if this item can be visually activated (defaults to true)
         */
        canActivate : true,
        /**
         * @cfg {Number} showDelay Length of time in milliseconds to wait before showing this item (defaults to 200)
         */
        showDelay: 200,
        // doc'd in BaseItem
        hideDelay: 200,

        // private
        ctype: 'Ext.menu.Item',

        // private
        onRender : function(container, position){
            if (!this.itemTpl) {
                this.itemTpl = Ext.menu.Item.prototype.itemTpl = new Ext.XTemplate(
                    '',
                            ' target="{hrefTarget}"',
                        '',
                     '>',
                         '',
                         '{text}',
                     ''
                 );
            }
            var a = this.getTemplateArgs();
            this.el = position ? this.itemTpl.insertBefore(position, a, true) : this.itemTpl.append(container, a, true);
            this.iconEl = this.el.child('img.x-menu-item-icon');
            this.textEl = this.el.child('.x-menu-item-text');
            Ext.menu.Item.superclass.onRender.call(this, container, position);
        },

        getTemplateArgs: function() {
            return {
                id: this.id,
                cls: this.itemCls + (this.menu ?  ' x-menu-item-arrow' : '') + (this.cls ?  ' ' + this.cls : ''),
                href: this.href || '#',
                hrefTarget: this.hrefTarget,
                icon: this.icon || Ext.BLANK_IMAGE_URL,
                iconCls: this.iconCls || '',
                text: this.itemText||this.text||' '
            };
        },

        /**
         * Sets the text to display in this menu item
         * @param {String} text The text to display
         */
        setText : function(text){
            this.text = text||' ';
            if(this.rendered){
                this.textEl.update(this.text);
                this.parentMenu.layout.doAutoSize();
            }
        },

        /**
         * Sets the CSS class to apply to the item's icon element
         * @param {String} cls The CSS class to apply
         */
        setIconClass : function(cls){
            var oldCls = this.iconCls;
            this.iconCls = cls;
            if(this.rendered){
                this.iconEl.replaceClass(oldCls, this.iconCls);
            }
        },

        //private
        beforeDestroy: function(){
            if (this.menu){
                this.menu.destroy();
            }
            Ext.menu.Item.superclass.beforeDestroy.call(this);
        },

        // private
        handleClick : function(e){
            if(!this.href){ // if no link defined, stop the event automatically
                e.stopEvent();
            }
            Ext.menu.Item.superclass.handleClick.apply(this, arguments);
        },

        // private
        activate : function(autoExpand){
            if(Ext.menu.Item.superclass.activate.apply(this, arguments)){
                this.focus();
                if(autoExpand){
                    this.expandMenu();
                }
            }
            return true;
        },

        // private
        shouldDeactivate : function(e){
            if(Ext.menu.Item.superclass.shouldDeactivate.call(this, e)){
                if(this.menu && this.menu.isVisible()){
                    return !this.menu.getEl().getRegion().contains(e.getPoint());
                }
                return true;
            }
            return false;
        },

        // private
        deactivate : function(){
            Ext.menu.Item.superclass.deactivate.apply(this, arguments);
            this.hideMenu();
        },

        // private
        expandMenu : function(autoActivate){
            if(!this.disabled && this.menu){
                clearTimeout(this.hideTimer);
                delete this.hideTimer;
                if(!this.menu.isVisible() && !this.showTimer){
                    this.showTimer = this.deferExpand.defer(this.showDelay, this, [autoActivate]);
                }else if (this.menu.isVisible() && autoActivate){
                    this.menu.tryActivate(0, 1);
                }
            }
        },

        // private
        deferExpand : function(autoActivate){
            delete this.showTimer;
            this.menu.show(this.container, this.parentMenu.subMenuAlign || 'tl-tr?', this.parentMenu);
            if(autoActivate){
                this.menu.tryActivate(0, 1);
            }
        },

        // private
        hideMenu : function(){
            clearTimeout(this.showTimer);
            delete this.showTimer;
            if(!this.hideTimer && this.menu && this.menu.isVisible()){
                this.hideTimer = this.deferHide.defer(this.hideDelay, this);
            }
        },

        // private
        deferHide : function(){
            delete this.hideTimer;
            if(this.menu.over){
                this.parentMenu.setActiveItem(this, false);
            }else{
                this.menu.hide();
            }
        }
    });
    Ext.reg('menuitem', Ext.menu.Item);