var numberField = new Ext.form.TextField({
    fieldLabel: 'Policy Number',
    name: 'numberField',
    labelStyle: 'width:125px;margin-right:10px;font-weight:bold;text-align:right;',
    labelSeparator: '...',
    width: 200
});
var btnOne = new Ext.Button({
    text: 'Change to "Claim number"',
    width: 150,
    style: 'margin:15px',
    handler: function() {
        numberField.setFieldLabel('Claim number');
    }
});
var btnTwo = new Ext.Button({
    text: 'Change to "Policy number"',
    width: 150,
    style: 'margin:15px',
    handler: function() {
        numberField.setFieldLabel('Policy number');
    }
});
var myFieldSet = new Ext.form.FieldSet({
    //title: 'a fieldset',
    bodyStyle: 'padding:15px',
    height: 100,
    items: [numberField,
            {
                xtype: 'panel',
                layout: 'table',
                columns: 2,
                style: 'margin:3px 10px',
                items: [btnOne , btnTwo]
            }
    ]
});
var theCode = new Ext.Panel({
    name: 'theCode',
    contentEl: 'setFieldLabelCode',
    height: 300,
    autoScroll: true,
    listeners: {
        afterrender: function() {
            Ext.get('setFieldLabelCode').dom.style.display = '';
        }
    }
});
var theCodeFieldSet = new Ext.form.FieldSet({
    title: ' The code ',
    layout: 'fit',
    items: theCode
});
var myForm = new Ext.form.FormPanel({
    frame: true,
    items: [myFieldSet,theCodeFieldSet]
});
var myWindow;
if (!myWindow) {
    myWindow = new Ext.Window({
        layout: 'form',
        width: 750,
        autoHeight: true,
        title: "Changing field label with setFieldLabel() method",
        closable: true,
        closeAction: 'hide',
        buttonAlign: 'left',
        animateTarget: 'setFieldLabelLink',
        modal: true,
        items: [myForm]
    })
}
var btnShowWindow = new Ext.Button({
    text: 'Show window',
    width:150,
    height:75,
    handler: function() {
        myWindow.show();
    }
});
function showExample( item ) {
    // if (item == 'setFieldLabel') {}
    myWindow.show();
}