The source code

    /**
     * @class Ext.layout.AccordionLayout
     * @extends Ext.layout.FitLayout
     * <p>This is a layout that manages multiple Panels in an expandable accordion style such that only
     * <b>one Panel can be expanded at any given time</b>. Each Panel has built-in support for expanding and collapsing.</p>
     * <p>Note: Only Ext.Panels <b>and all subclasses of Ext.Panel</b> may be used in an accordion layout Container.</p>
     * <p>This class is intended to be extended or created via the <tt><b>{@link Ext.Container#layout layout}</b></tt>
     * configuration property.  See <tt><b>{@link Ext.Container#layout}</b></tt> for additional details.</p>
     * <p>Example usage:</p>
     * <pre><code>
    var accordion = new Ext.Panel({
        title: 'Accordion Layout',
        layout:'accordion',
        defaults: {
            // applied to each contained panel
            bodyStyle: 'padding:15px'
        },
        layoutConfig: {
            // layout-specific configs go here
            titleCollapse: false,
            animate: true,
            activeOnTop: true
        },
        items: [{
            title: 'Panel 1',
            html: '&lt;p&gt;Panel content!&lt;/p&gt;'
        },{
            title: 'Panel 2',
            html: '&lt;p&gt;Panel content!&lt;/p&gt;'
        },{
            title: 'Panel 3',
            html: '&lt;p&gt;Panel content!&lt;/p&gt;'
        }]
    });
    </code></pre>
     */
    Ext.layout.AccordionLayout = Ext.extend(Ext.layout.FitLayout, {
        /**
         * @cfg {Boolean} fill
         * True to adjust the active item's height to fill the available space in the container, false to use the
         * item's current height, or auto height if not explicitly set (defaults to true).
         */
        fill : true,
        /**
         * @cfg {Boolean} autoWidth
         * True to set each contained item's width to 'auto', false to use the item's current width (defaults to true).
         * Note that some components, in particular the {@link Ext.grid.GridPanel grid}, will not function properly within
         * layouts if they have auto width, so in such cases this config should be set to false.
         */
        autoWidth : true,
        /**
         * @cfg {Boolean} titleCollapse
         * True to allow expand/collapse of each contained panel by clicking anywhere on the title bar, false to allow
         * expand/collapse only when the toggle tool button is clicked (defaults to true).  When set to false,
         * {@link #hideCollapseTool} should be false also.
         */
        titleCollapse : true,
        /**
         * @cfg {Boolean} hideCollapseTool
         * True to hide the contained panels' collapse/expand toggle buttons, false to display them (defaults to false).
         * When set to true, {@link #titleCollapse} should be true also.
         */
        hideCollapseTool : false,
        /**
         * @cfg {Boolean} collapseFirst
         * True to make sure the collapse/expand toggle button always renders first (to the left of) any other tools
         * in the contained panels' title bars, false to render it last (defaults to false).
         */
        collapseFirst : false,
        /**
         * @cfg {Boolean} animate
         * True to slide the contained panels open and closed during expand/collapse using animation, false to open and
         * close directly with no animation (defaults to false).  Note: to defer to the specific config setting of each
         * contained panel for this property, set this to undefined at the layout level.
         */
        animate : false,
        /**
         * @cfg {Boolean} sequence
         * <b>Experimental</b>. If animate is set to true, this will result in each animation running in sequence.
         */
        sequence : false,
        /**
         * @cfg {Boolean} activeOnTop
         * True to swap the position of each panel as it is expanded so that it becomes the first item in the container,
         * false to keep the panels in the rendered order. <b>This is NOT compatible with "animate:true"</b> (defaults to false).
         */
        activeOnTop : false,

        type: 'accordion',

        renderItem : function(c){
            if(this.animate === false){
                c.animCollapse = false;
            }
            c.collapsible = true;
            if(this.autoWidth){
                c.autoWidth = true;
            }
            if(this.titleCollapse){
                c.titleCollapse = true;
            }
            if(this.hideCollapseTool){
                c.hideCollapseTool = true;
            }
            if(this.collapseFirst !== undefined){
                c.collapseFirst = this.collapseFirst;
            }
            if(!this.activeItem && !c.collapsed){
                this.setActiveItem(c, true);
            }else if(this.activeItem && this.activeItem != c){
                c.collapsed = true;
            }
            Ext.layout.AccordionLayout.superclass.renderItem.apply(this, arguments);
            c.header.addClass('x-accordion-hd');
            c.on('beforeexpand', this.beforeExpand, this);
        },

        onRemove: function(c){
            Ext.layout.AccordionLayout.superclass.onRemove.call(this, c);
            if(c.rendered){
                c.header.removeClass('x-accordion-hd');
            }
            c.un('beforeexpand', this.beforeExpand, this);
        },

        // private
        beforeExpand : function(p, anim){
            var ai = this.activeItem;
            if(ai){
                if(this.sequence){
                    delete this.activeItem;
                    if (!ai.collapsed){
                        ai.collapse({callback:function(){
                            p.expand(anim || true);
                        }, scope: this});
                        return false;
                    }
                }else{
                    ai.collapse(this.animate);
                }
            }
            this.setActive(p);
            if(this.activeOnTop){
                p.el.dom.parentNode.insertBefore(p.el.dom, p.el.dom.parentNode.firstChild);
            }
            // Items have been hidden an possibly rearranged, we need to get the container size again.
            this.layout();
        },

        // private
        setItemSize : function(item, size){
            if(this.fill && item){
                var hh = 0, i, ct = this.getRenderedItems(this.container), len = ct.length, p;
                // Add up all the header heights
                for (i = 0; i < len; i++) {
                    if((p = ct[i]) != item && !p.hidden){
                        hh += p.header.getHeight();
                    }
                };
                // Subtract the header heights from the container size
                size.height -= hh;
                // Call setSize on the container to set the correct height.  For Panels, deferedHeight
                // will simply store this size for when the expansion is done.
                item.setSize(size);
            }
        },

        /**
         * Sets the active (expanded) item in the layout.
         * @param {String/Number} item The string component id or numeric index of the item to activate
         */
        setActiveItem : function(item){
            this.setActive(item, true);
        },

        // private
        setActive : function(item, expand){
            var ai = this.activeItem;
            item = this.container.getComponent(item);
            if(ai != item){
                if(item.rendered && item.collapsed && expand){
                    item.expand();
                }else{
                    if(ai){
                       ai.fireEvent('deactivate', ai);
                    }
                    this.activeItem = item;
                    item.fireEvent('activate', item);
                }
            }
        }
    });
    Ext.Container.LAYOUTS.accordion = Ext.layout.AccordionLayout;

    //backwards compat
    Ext.layout.Accordion = Ext.layout.AccordionLayout;