The source code

    /*!
     * Ext JS Library 3.2.1
     * Copyright(c) 2006-2010 Ext JS, Inc.
     * licensing@extjs.com
     * http://www.extjs.com/license
     */
    /**
     * @class Ext.layout.AutoLayout
     * The AutoLayout is the default layout manager delegated by {@link Ext.Container} to
     * render any child Components when no {@link Ext.Container#layout layout} is configured into
     * a {@link Ext.Container Container}..  AutoLayout provides only a passthrough of any layout calls
     * to any child containers.
     */
    Ext.layout.AutoLayout = Ext.extend(Ext.layout.ContainerLayout, {
        type: 'auto',

        monitorResize: true,

        onLayout : function(ct, target){
            Ext.layout.AutoLayout.superclass.onLayout.call(this, ct, target);
            var cs = this.getRenderedItems(ct), len = cs.length, i, c;
            for(i = 0; i < len; i++){
                c = cs[i];
                if (c.doLayout){
                    // Shallow layout children
                    c.doLayout(true);
                }
            }
        }
    });

    Ext.Container.LAYOUTS['auto'] = Ext.layout.AutoLayout;