Tag field add new value

HTML

<script src="http://dev.sencha.com/extjs/5.1.0/examples/shared/include-ext.js"></script>

JavaScript

Ext.onReady(function () {

    Ext.QuickTips.init();

    Ext.create('Ext.container.Viewport', {
        layout: 'fit',
        padding: 100,
        items: [{
            items: [{
                width: 400,
                xtype: 'tagfield',
                store: ['existing item', 'another existing item'],
                queryMode: 'local',
                forceSelection: false,
                autocomplete: 'off'

            }]
        }]
    });
});