Sencha ExtJS, Element, DOM, down, and textfield

This Sencha ExtJS code snippet shows how to use the Ext.Element down method to get the value from a textfield:

{
    xtype: 'button',
    text: 'Save',
    listeners: {
        click: function () { 
            // fname = Ext.get('first_name').dom.value;
            var fname = myForm.down('textfield[name=first_name]').getValue();    
            alert(fname);
        }
    }
}

I found the code at the link shown. Mostly I want to remember how to use the down method/function with a textfield. (I'm just learning about Sencha selectors, how it shows the DOM, and the Ext.Element class.