The source code

    (function(){
    Ext.ns('Ext.a11y');

    Ext.a11y.Frame = Ext.extend(Object, {
        initialized: false,

        constructor: function(size, color){
            this.setSize(size || 1);
            this.setColor(color || '15428B');
        },

        init: function(){
            if (!this.initialized) {
                this.sides = [];

                var s, i;

                this.ct = Ext.DomHelper.append(document.body, {
                    cls: 'x-a11y-focusframe'
                }, true);

                for (i = 0; i < 4; i++) {
                    s = Ext.DomHelper.append(this.ct, {
                        cls: 'x-a11y-focusframe-side',
                        style: 'background-color: #' + this.color
                    }, true);
                    s.visibilityMode = Ext.Element.DISPLAY;
                    this.sides.push(s);
                }

                this.frameTask = new Ext.util.DelayedTask(function(el){
                    var newEl = Ext.get(el);
                    if (newEl != this.curEl) {
                        var w = newEl.getWidth();
                        var h = newEl.getHeight();
                        this.sides[0].show().setSize(w, this.size).anchorTo(el, 'tl', [0, -1]);
                        this.sides[2].show().setSize(w, this.size).anchorTo(el, 'bl', [0, -1]);
                        this.sides[1].show().setSize(this.size, h).anchorTo(el, 'tr', [-1, 0]);
                        this.sides[3].show().setSize(this.size, h).anchorTo(el, 'tl', [-1, 0]);
                        this.curEl = newEl;
                    }
                }, this);

                this.unframeTask = new Ext.util.DelayedTask(function(){
                    if (this.initialized) {
                        this.sides[0].hide();
                        this.sides[1].hide();
                        this.sides[2].hide();
                        this.sides[3].hide();
                        this.curEl = null;
                    }
                }, this);
                this.initialized = true;
            }
        },

        frame: function(el){
            this.init();
            this.unframeTask.cancel();
            this.frameTask.delay(2, false, false, [el]);
        },

        unframe: function(){
            this.init();
            this.unframeTask.delay(2);
        },

        setSize: function(size){
            this.size = size;
        },

        setColor: function(color){
            this.color = color;
        }
    });

    Ext.a11y.FocusFrame = new Ext.a11y.Frame(2, '15428B');
    Ext.a11y.RelayFrame = new Ext.a11y.Frame(1, '6B8CBF');

    Ext.a11y.Focusable = Ext.extend(Ext.util.Observable, {
        constructor: function(el, relayTo, noFrame, frameEl){
            Ext.a11y.Focusable.superclass.constructor.call(this);

            this.addEvents('focus', 'blur', 'left', 'right', 'up', 'down', 'esc', 'enter', 'space');

            if (el instanceof Ext.Component) {
                this.el = el.el;
                this.setComponent(el);
            }
            else {
                this.el = Ext.get(el);
                this.setComponent(null);
            }

            this.setRelayTo(relayTo)
            this.setNoFrame(noFrame);
            this.setFrameEl(frameEl);

            this.init();

            Ext.a11y.FocusMgr.register(this);
        },

        init: function(){
            this.el.dom.tabIndex = '1';
            this.el.addClass('x-a11y-focusable');
            this.el.on({
                focus: this.onFocus,
                blur: this.onBlur,
                keydown: this.onKeyDown,
                scope: this
            });
        },

        setRelayTo: function(relayTo){
            this.relayTo = relayTo ? Ext.a11y.FocusMgr.get(relayTo) : null;
        },

        setNoFrame: function(noFrame){
            this.noFrame = (noFrame === true) ? true : false;
        },

        setFrameEl: function(frameEl){
            this.frameEl = frameEl && Ext.get(frameEl) || this.el;
        },

        setComponent: function(cmp){
            this.component = cmp || null;
        },

        onKeyDown: function(e, t){
            var k = e.getKey(), SK = Ext.a11y.Focusable.SpecialKeys, ret, tf;

            tf = (t !== this.el.dom) ? Ext.a11y.FocusMgr.get(t, true) : this;
            if (!tf) {
                // this can happen when you are on a focused item within a panel body
                // that is not a Ext.a11y.Focusable
                tf = Ext.a11y.FocusMgr.get(Ext.fly(t).parent('.x-a11y-focusable'));
            }

            if (SK[k] !== undefined) {
                ret = this.fireEvent(SK[k], e, t, tf, this);
            }
            if (ret === false || this.fireEvent('keydown', e, t, tf, this) === false) {
                e.stopEvent();
            }
        },

        focus: function(){
            this.el.dom.focus();
        },

        blur: function(){
            this.el.dom.blur();
        },

        onFocus: function(e, t){
            this.el.addClass('x-a11y-focused');
            if (this.relayTo) {
                this.relayTo.el.addClass('x-a11y-focused-relay');
                if (!this.relayTo.noFrame) {
                    Ext.a11y.FocusFrame.frame(this.relayTo.frameEl);
                }
                if (!this.noFrame) {
                    Ext.a11y.RelayFrame.frame(this.frameEl);
                }
            }
            else {
                if (!this.noFrame) {
                    Ext.a11y.FocusFrame.frame(this.frameEl);
                }
            }

            this.fireEvent('focus', e, t, this);
        },

        onBlur: function(e, t){
            if (this.relayTo) {
                this.relayTo.el.removeClass('x-a11y-focused-relay');
                Ext.a11y.RelayFrame.unframe();
            }
            this.el.removeClass('x-a11y-focused');
            Ext.a11y.FocusFrame.unframe();
            this.fireEvent('blur', e, t, this);
        },

        destroy: function(){
            this.el.un('keydown', this.onKeyDown);
            this.el.un('focus', this.onFocus);
            this.el.un('blur', this.onBlur);
            this.el.removeClass('x-a11y-focusable');
            this.el.removeClass('x-a11y-focused');
            if (this.relayTo) {
                this.relayTo.el.removeClass('x-a11y-focused-relay');
            }
        }
    });

    Ext.a11y.FocusItem = Ext.extend(Object, {
        constructor: function(el, enableTabbing){
            Ext.a11y.FocusItem.superclass.constructor.call(this);

            this.el = Ext.get(el);
            this.fi = new Ext.a11y.Focusable(el);
            this.fi.setComponent(this);

            this.fi.on('tab', this.onTab, this);

            this.enableTabbing = enableTabbing === true ? true : false;
        },

        getEnterItem: function(){
            if (this.enableTabbing) {
                var items = this.getFocusItems();
                if (items && items.length) {
                    return items[0];
                }
            }
        },

        getFocusItems: function(){
            if (this.enableTabbing) {
                return this.el.query('a, button, input, select');
            }
            return null;
        },

        onTab: function(e, t){
            var items = this.getFocusItems(), i;

            if (items && items.length && (i = items.indexOf(t)) !== -1) {
                if (e.shiftKey && i > 0) {
                    e.stopEvent();
                    items[i - 1].focus();
                    Ext.a11y.FocusFrame.frame.defer(20, Ext.a11y.FocusFrame, [this.el]);
                    return;
                }
                else
                    if (!e.shiftKey && i < items.length - 1) {
                        e.stopEvent();
                        items[i + 1].focus();
                        Ext.a11y.FocusFrame.frame.defer(20, Ext.a11y.FocusFrame, [this.el]);
                        return;
                    }
            }
        },

        focus: function(){
            if (this.enableTabbing) {
                var items = this.getFocusItems();
                if (items && items.length) {
                    items[0].focus();
                    Ext.a11y.FocusFrame.frame.defer(20, Ext.a11y.FocusFrame, [this.el]);
                    return;
                }
            }
            this.fi.focus();
        },

        blur: function(){
            this.fi.blur();
        }
    });

    Ext.a11y.FocusMgr = function(){
        var all = new Ext.util.MixedCollection();

        return {
            register: function(f){
                all.add(f.el && Ext.id(f.el), f);
            },

            unregister: function(f){
                all.remove(f);
            },

            get: function(el, noCreate){
                return all.get(Ext.id(el)) || (noCreate ? false : new Ext.a11y.Focusable(el));
            },

            all: all
        }
    }();

    Ext.a11y.Focusable.SpecialKeys = {};
    Ext.a11y.Focusable.SpecialKeys[Ext.EventObjectImpl.prototype.LEFT] = 'left';
    Ext.a11y.Focusable.SpecialKeys[Ext.EventObjectImpl.prototype.RIGHT] = 'right';
    Ext.a11y.Focusable.SpecialKeys[Ext.EventObjectImpl.prototype.DOWN] = 'down';
    Ext.a11y.Focusable.SpecialKeys[Ext.EventObjectImpl.prototype.UP] = 'up';
    Ext.a11y.Focusable.SpecialKeys[Ext.EventObjectImpl.prototype.ESC] = 'esc';
    Ext.a11y.Focusable.SpecialKeys[Ext.EventObjectImpl.prototype.ENTER] = 'enter';
    Ext.a11y.Focusable.SpecialKeys[Ext.EventObjectImpl.prototype.SPACE] = 'space';
    Ext.a11y.Focusable.SpecialKeys[Ext.EventObjectImpl.prototype.TAB] = 'tab';

    // we use the new observeClass method to fire our new initFocus method on components
    Ext.util.Observable.observeClass(Ext.Component);
    Ext.Component.on('render', function(cmp){
        cmp.initFocus();
        cmp.initARIA();
    });
    Ext.override(Ext.Component, {
        initFocus: Ext.emptyFn,
        initARIA: Ext.emptyFn
    });

    Ext.override(Ext.Container, {
        isFocusable: true,
        noFocus: false,

        // private
        initFocus: function(){
            if (!this.fi && !this.noFocus) {
                this.fi = new Ext.a11y.Focusable(this);
            }
            this.mon(this.fi, {
                focus: this.onFocus,
                blur: this.onBlur,
                tab: this.onTab,
                enter: this.onEnter,
                esc: this.onEsc,
                scope: this
            });

            if (this.hidden) {
                this.isFocusable = false;
            }

            this.on('show', function(){
                this.isFocusable = true;
            }, this);
            this.on('hide', function(){
                this.isFocusable = false;
            }, this);
        },

        focus: function(){
            this.fi.focus();
        },

        blur: function(){
            this.fi.blur();
        },

        enter: function(){
            var eitem = this.getEnterItem();
            if (eitem) {
                eitem.focus();
            }
        },

        onFocus: Ext.emptyFn,
        onBlur: Ext.emptyFn,

        onTab: function(e, t, tf){
            var rf = tf.relayTo || tf;
            if (rf.component && rf.component !== this) {
                e.stopEvent();
                var item = e.shiftKey ? this.getPreviousFocus(rf.component) : this.getNextFocus(rf.component);
                item.focus();
            }
        },

        onEnter: function(e, t, tf){
            // check to see if enter is pressed while "on" the panel
            if (tf.component && tf.component === this) {
                e.stopEvent();
                this.enter();
            }
            e.stopPropagation();
        },

        onEsc: function(e, t){
            e.preventDefault();

            // check to see if esc is pressed while "inside" the panel
            // or while "on" the panel
            if (t === this.el.dom) {
                // "on" the panel, check if this panel has an owner panel and focus that
                // we dont stop the event in this case so that this same check will be
                // done for this ownerCt
                if (this.ownerCt) {
                    this.ownerCt.focus();
                }
            }
            else {
                // we were inside the panel when esc was pressed,
                // so go back "on" the panel
                if (this.ownerCt && this.ownerCt.isFocusable) {
                    var si = this.ownerCt.getFocusItems();

                    if (si && si.getCount() > 1) {
                        e.stopEvent();
                    }
                }
                this.focus();
            }
        },

        getFocusItems: function(){
            return this.items &&
            this.items.filterBy(function(o){
                return o.isFocusable;
            }) ||
            null;
        },

        getEnterItem: function(){
            var ci = this.getFocusItems(), length = ci ? ci.getCount() : 0;

            if (length === 1) {
                return ci.first().getEnterItem && ci.first().getEnterItem() || ci.first();
            }
            else
                if (length > 1) {
                    return ci.first();
                }
        },

        getNextFocus: function(current){
            var items = this.getFocusItems(), next = current, i = items.indexOf(current), length = items.getCount();

            if (i === length - 1) {
                next = items.first();
            }
            else {
                next = items.get(i + 1);
            }
            return next;
        },

        getPreviousFocus: function(current){
            var items = this.getFocusItems(), prev = current, i = items.indexOf(current), length = items.getCount();

            if (i === 0) {
                prev = items.last();
            }
            else {
                prev = items.get(i - 1);
            }
            return prev;
        },

        getFocusable : function() {
            return this.fi;
        }
    });

    Ext.override(Ext.Panel, {
        /**
         * @cfg {Boolean} enableTabbing true to enable tabbing. Default is false.
         */
        getFocusItems: function(){
            // items gets all the items inside the body
            var items = Ext.Panel.superclass.getFocusItems.call(this), bodyFocus = null;

            if (!items) {
                items = new Ext.util.MixedCollection();
                this.bodyFocus = this.bodyFocus || new Ext.a11y.FocusItem(this.body, this.enableTabbing);
                items.add('body', this.bodyFocus);
            }
            // but panels can also have tbar, bbar, fbar
            if (this.tbar && this.topToolbar) {
                items.insert(0, this.topToolbar);
            }
            if (this.bbar && this.bottomToolbar) {
                items.add(this.bottomToolbar);
            }
            if (this.fbar) {
                items.add(this.fbar);
            }

            return items;
        }
    });

    Ext.override(Ext.TabPanel, {
        // private
        initFocus: function(){
            Ext.TabPanel.superclass.initFocus.call(this);
            this.mon(this.fi, {
                left: this.onLeft,
                right: this.onRight,
                scope: this
            });
        },

        onLeft: function(e){
            if (!this.activeTab) {
                return;
            }
            e.stopEvent();
            var prev = this.items.itemAt(this.items.indexOf(this.activeTab) - 1);
            if (prev) {
                this.setActiveTab(prev);
            }
            return false;
        },

        onRight: function(e){
            if (!this.activeTab) {
                return;
            }
            e.stopEvent();
            var next = this.items.itemAt(this.items.indexOf(this.activeTab) + 1);
            if (next) {
                this.setActiveTab(next);
            }
            return false;
        }
    });

    Ext.override(Ext.tree.TreeNodeUI, {
        // private
        focus: function(){
            this.node.getOwnerTree().bodyFocus.focus();
        }
    });

    Ext.override(Ext.tree.TreePanel, {
        // private
        afterRender : function(){
            Ext.tree.TreePanel.superclass.afterRender.call(this);
            this.root.render();
            if(!this.rootVisible){
                this.root.renderChildren();
            }
            this.bodyFocus = new Ext.a11y.FocusItem(this.body.down('.x-tree-root-ct'));
            this.bodyFocus.fi.setFrameEl(this.body);
        }
    });

    Ext.override(Ext.grid.GridPanel, {
        initFocus: function(){
            Ext.grid.GridPanel.superclass.initFocus.call(this);
            this.bodyFocus = new Ext.a11y.FocusItem(this.view.focusEl);
            this.bodyFocus.fi.setFrameEl(this.body);
        }
    });

    Ext.override(Ext.Button, {
        isFocusable: true,
        noFocus: false,

        initFocus: function(){
            Ext.Button.superclass.initFocus.call(this);
            this.fi = this.fi || new Ext.a11y.Focusable(this.btnEl, null, null, this.el);
            this.fi.setComponent(this);

            this.mon(this.fi, {
                focus: this.onFocus,
                blur: this.onBlur,
                scope: this
            });

            if (this.menu) {
                this.mon(this.fi, 'down', this.showMenu, this);
                this.on('menuhide', this.focus, this);
            }

            if (this.hidden) {
                this.isFocusable = false;
            }

            this.on('show', function(){
                this.isFocusable = true;
            }, this);
            this.on('hide', function(){
                this.isFocusable = false;
            }, this);
        },

        focus: function(){
            this.fi.focus();
        },

        blur: function(){
            this.fi.blur();
        },

        onFocus: function(){
            if (!this.disabled) {
                this.el.addClass("x-btn-focus");
            }
        },

        onBlur: function(){
            this.el.removeClass("x-btn-focus");
        }
    });

    Ext.override(Ext.Toolbar, {
        initFocus: function(){
            Ext.Toolbar.superclass.initFocus.call(this);
            this.mon(this.fi, {
                left: this.onLeft,
                right: this.onRight,
                scope: this
            });

            this.on('focus', this.onButtonFocus, this, {
                stopEvent: true
            });
        },

        addItem: function(item){
            Ext.Toolbar.superclass.add.apply(this, arguments);
            if (item.rendered && item.fi !== undefined) {
                item.fi.setRelayTo(this.el);
                this.relayEvents(item.fi, ['focus']);
            }
            else {
                item.on('render', function(){
                    if (item.fi !== undefined) {
                        item.fi.setRelayTo(this.el);
                        this.relayEvents(item.fi, ['focus']);
                    }
                }, this, {
                    single: true
                });
            }
            return item;
        },

        onFocus: function(){
            var items = this.getFocusItems();
            if (items && items.getCount() > 0) {
                if (this.lastFocus && items.indexOf(this.lastFocus) !== -1) {
                    this.lastFocus.focus();
                }
                else {
                    items.first().focus();
                }
            }
        },

        onButtonFocus: function(e, t, tf){
            this.lastFocus = tf.component || null;
        },

        onLeft: function(e, t, tf){
            e.stopEvent();
            this.getPreviousFocus(tf.component).focus();
        },

        onRight: function(e, t, tf){
            e.stopEvent();
            this.getNextFocus(tf.component).focus();
        },

        getEnterItem: Ext.emptyFn,
        onTab: Ext.emptyFn,
        onEsc: Ext.emptyFn
    });

    Ext.override(Ext.menu.BaseItem, {
        initFocus: function(){
            this.fi = new Ext.a11y.Focusable(this, this.parentMenu && this.parentMenu.el || null, true);
        }
    });

    Ext.override(Ext.menu.Menu, {
        initFocus: function(){
            this.fi = new Ext.a11y.Focusable(this);
            this.focusEl = this.fi;
        }
    });

    Ext.a11y.WindowMgr = new Ext.WindowGroup();

    Ext.apply(Ext.WindowMgr, {
        bringToFront: function(win){
            Ext.a11y.WindowMgr.bringToFront.call(this, win);
            if (win.modal) {
                win.enter();
            }
            else {
                win.focus();
            }
        }
    });

    Ext.override(Ext.Window, {
        initFocus: function(){
            Ext.Window.superclass.initFocus.call(this);
            this.on('beforehide', function(){
                Ext.a11y.RelayFrame.unframe();
                Ext.a11y.FocusFrame.unframe();
            });
        }
    });

    Ext.override(Ext.form.Field, {
        isFocusable: true,
        noFocus: false,

        initFocus: function(){
            this.fi = this.fi || new Ext.a11y.Focusable(this, null, true);

            Ext.form.Field.superclass.initFocus.call(this);

            if (this.hidden) {
                this.isFocusable = false;
            }

            this.on('show', function(){
                this.isFocusable = true;
            }, this);
            this.on('hide', function(){
                this.isFocusable = false;
            }, this);
        }
    });

    Ext.override(Ext.FormPanel, {
        initFocus: function(){
            Ext.FormPanel.superclass.initFocus.call(this);
            this.on('focus', this.onFieldFocus, this, {
                stopEvent: true
            });
        },

        // private
        createForm: function(){
            delete this.initialConfig.listeners;
            var form = new Ext.form.BasicForm(null, this.initialConfig);
            form.afterMethod('add', this.formItemAdd, this);
            return form;
        },

        formItemAdd: function(item){
            item.on('render', function(field){
                field.fi.setRelayTo(this.el);
                this.relayEvents(field.fi, ['focus']);
            }, this, {
                single: true
            });
        },

        onFocus: function(){
            var items = this.getFocusItems();
            if (items && items.getCount() > 0) {
                if (this.lastFocus && items.indexOf(this.lastFocus) !== -1) {
                    this.lastFocus.focus();
                }
                else {
                    items.first().focus();
                }
            }
        },

        onFieldFocus: function(e, t, tf){
            this.lastFocus = tf.component || null;
        },

        onTab: function(e, t, tf){
            if (tf.relayTo.component === this) {
                var item = e.shiftKey ? this.getPreviousFocus(tf.component) : this.getNextFocus(tf.component);

                if (item) {
                    ev.stopEvent();
                    item.focus();
                    return;
                }
            }
            Ext.FormPanel.superclass.onTab.apply(this, arguments);
        },

        getNextFocus: function(current){
            var items = this.getFocusItems(), i = items.indexOf(current), length = items.getCount();

            return (i < length - 1) ? items.get(i + 1) : false;
        },

        getPreviousFocus: function(current){
            var items = this.getFocusItems(), i = items.indexOf(current), length = items.getCount();

            return (i > 0) ? items.get(i - 1) : false;
        }
    });

    Ext.override(Ext.Viewport, {
        initFocus: function(){
            Ext.Viewport.superclass.initFocus.apply(this);
            this.mon(Ext.get(document), 'focus', this.focus, this);
            this.mon(Ext.get(document), 'blur', this.blur, this);
            this.fi.setNoFrame(true);
        },

        onTab: function(e, t, tf, f){
            e.stopEvent();

            if (tf === f) {
                items = this.getFocusItems();
                if (items && items.getCount() > 0) {
                    items.first().focus();
                }
            }
            else {
                var rf = tf.relayTo || tf;
                var item = e.shiftKey ? this.getPreviousFocus(rf.component) : this.getNextFocus(rf.component);
                item.focus();
            }
        }
    });

    })();