The source code

    FeedWindow = function() {
        this.feedUrl = new Ext.form.ComboBox({
            id: 'feed-url',
            fieldLabel: 'Enter the URL of the feed to add',
            emptyText: 'http://example.com/blog/feed',
            width: 450,
            validationEvent: false,
            validateOnBlur: false,
            msgTarget: 'under',
            triggerAction: 'all',
            displayField: 'url',
            mode: 'local',

            listeners:{
                valid: this.syncShadow,
                invalid: this.syncShadow,
                scope: this
            },
            tpl: new Ext.XTemplate(
                    '',
                    '{url}{text}',
                    '',
                    ''),
            store: new Ext.data.ArrayStore({
                fields: ['url', 'text'],
                data : this.defaultFeeds
            })
        });

        this.form = new Ext.FormPanel({
            labelAlign:'top',
            items:this.feedUrl,
            border: false,
            bodyStyle:'background:transparent;padding:10px;'
        });

        FeedWindow.superclass.constructor.call(this, {
            title: 'Add Feed',
            iconCls: 'feed-icon',
            id: 'add-feed-win',
            autoHeight: true,
            width: 500,
            resizable: false,
            plain:true,
            modal: true,
            y: 100,
            autoScroll: true,
            closeAction: 'hide',

            buttons:[{
                text: 'Add Feed!',
                handler: this.onAdd,
                scope: this
            },{
                text: 'Cancel',
                handler: this.hide.createDelegate(this, [])
            }],

            items: this.form
        });

        this.addEvents({add:true});
    }

    Ext.extend(FeedWindow, Ext.Window, {
        defaultFeeds : [
            ['http://www.divergingpath.com/rss.cfm?mode=full', 'Aaron Conran\'s Blog'],
            ['http://feeds.yuiblog.com/YahooUserInterfaceBlog',  'Yahoo! UI Blog'],
            ['http://feeds.feedburner.com/jquery/', 'jQuery Blog'],
            ['http://sports.yahoo.com/nba/rss.xml', 'NBA News'],
            ['http://feeds.dzone.com/dzone/frontpage', 'DZone.com']
        ],

        show : function(){
            if(this.rendered){
                this.feedUrl.setValue('');
            }
            FeedWindow.superclass.show.apply(this, arguments);
        },

        onAdd: function() {
            this.el.mask('Validating Feed...', 'x-mask-loading');
            var url = this.feedUrl.getValue();
            Ext.Ajax.request({
                url: 'feed-proxy.php',
                params: {feed: url},
                success: this.validateFeed,
                failure: this.markInvalid,
                scope: this,
                feedUrl: url
            });
        },

        markInvalid : function(){
            this.feedUrl.markInvalid('The URL specified is not a valid RSS2 feed.');
            this.el.unmask();
        },

        validateFeed : function(response, options){
            var dq = Ext.DomQuery;
            var url = options.feedUrl;

            try{
                var xml = response.responseXML;
                var channel = xml.getElementsByTagName('channel')[0];
                if(channel){
                    var text = dq.selectValue('title', channel, url);
                    var description = dq.selectValue('description', channel, 'No description available.');
                    this.el.unmask();
                    this.hide();

                    return this.fireEvent('validfeed', {
                        url: url,
                        text: text,
                        description: description
                    });
                }
            }catch(e){
            }
            this.markInvalid();
        }
    });