The source code

    /**
     * @class Ext.tree.TreeNodeUI
     * This class provides the default UI implementation for Ext TreeNodes.
     * The TreeNode UI implementation is separate from the
     * tree implementation, and allows customizing of the appearance of
     * tree nodes.<br>
     * <p>
     * If you are customizing the Tree's user interface, you
     * may need to extend this class, but you should never need to instantiate this class.<br>
     * <p>
     * This class provides access to the user interface components of an Ext TreeNode, through
     * {@link Ext.tree.TreeNode#getUI}
     */
    Ext.tree.TreeNodeUI = Ext.extend(Object, {

        constructor : function(node){
            Ext.apply(this, {
                node: node,
                rendered: false,
                animating: false,
                wasLeaf: true,
                ecc: 'x-tree-ec-icon x-tree-elbow',
                emptyIcon: Ext.BLANK_IMAGE_URL
            });
        },

        // private
        removeChild : function(node){
            if(this.rendered){
                this.ctNode.removeChild(node.ui.getEl());
            }
        },

        // private
        beforeLoad : function(){
             this.addClass("x-tree-node-loading");
        },

        // private
        afterLoad : function(){
             this.removeClass("x-tree-node-loading");
        },

        // private
        onTextChange : function(node, text, oldText){
            if(this.rendered){
                this.textNode.innerHTML = text;
            }
        },

        // private
        onIconClsChange : function(node, cls, oldCls){
            if(this.rendered){
                Ext.fly(this.iconNode).replaceClass(oldCls, cls);
            }
        },

        // private
        onIconChange : function(node, icon){
            if(this.rendered){
                //'<img src="', a.icon || this.emptyIcon, '" class="x-tree-node-icon',(a.icon ? " x-tree-node-inline-icon" : ""),(a.iconCls ? " "+a.iconCls : ""),'" unselectable="on" />',
                var empty = Ext.isEmpty(icon);
                this.iconNode.src = empty ? this.emptyIcon : icon;
                Ext.fly(this.iconNode)[empty ? 'removeClass' : 'addClass']('x-tree-node-inline-icon');
            }
        },

        // private
        onTipChange : function(node, tip, title){
            if(this.rendered){
                var hasTitle = Ext.isDefined(title);
                if(this.textNode.setAttributeNS){
                    this.textNode.setAttributeNS("ext", "qtip", tip);
                    if(hasTitle){
                        this.textNode.setAttributeNS("ext", "qtitle", title);
                    }
                }else{
                    this.textNode.setAttribute("ext:qtip", tip);
                    if(hasTitle){
                        this.textNode.setAttribute("ext:qtitle", title);
                    }
                }
            }
        },

        // private
        onHrefChange : function(node, href, target){
            if(this.rendered){
                this.anchor.href = this.getHref(href);
                if(Ext.isDefined(target)){
                    this.anchor.target = target;
                }
            }
        },

        // private
        onClsChange : function(node, cls, oldCls){
            if(this.rendered){
                Ext.fly(this.elNode).replaceClass(oldCls, cls);
            }
        },

        // private
        onDisableChange : function(node, state){
            this.disabled = state;
            if (this.checkbox) {
                this.checkbox.disabled = state;
            }
            this[state ? 'addClass' : 'removeClass']('x-tree-node-disabled');
        },

        // private
        onSelectedChange : function(state){
            if(state){
                this.focus();
                this.addClass("x-tree-selected");
            }else{
                //this.blur();
                this.removeClass("x-tree-selected");
            }
        },

        // private
        onMove : function(tree, node, oldParent, newParent, index, refNode){
            this.childIndent = null;
            if(this.rendered){
                var targetNode = newParent.ui.getContainer();
                if(!targetNode){//target not rendered
                    this.holder = document.createElement("div");
                    this.holder.appendChild(this.wrap);
                    return;
                }
                var insertBefore = refNode ? refNode.ui.getEl() : null;
                if(insertBefore){
                    targetNode.insertBefore(this.wrap, insertBefore);
                }else{
                    targetNode.appendChild(this.wrap);
                }
                this.node.renderIndent(true, oldParent != newParent);
            }
        },

    /**
     * Adds one or more CSS classes to the node's UI element.
     * Duplicate classes are automatically filtered out.
     * @param {String/Array} className The CSS class to add, or an array of classes
     */
        addClass : function(cls){
            if(this.elNode){
                Ext.fly(this.elNode).addClass(cls);
            }
        },

    /**
     * Removes one or more CSS classes from the node's UI element.
     * @param {String/Array} className The CSS class to remove, or an array of classes
     */
        removeClass : function(cls){
            if(this.elNode){
                Ext.fly(this.elNode).removeClass(cls);
            }
        },

        // private
        remove : function(){
            if(this.rendered){
                this.holder = document.createElement("div");
                this.holder.appendChild(this.wrap);
            }
        },

        // private
        fireEvent : function(){
            return this.node.fireEvent.apply(this.node, arguments);
        },

        // private
        initEvents : function(){
            this.node.on("move", this.onMove, this);

            if(this.node.disabled){
                this.onDisableChange(this.node, true);
            }
            if(this.node.hidden){
                this.hide();
            }
            var ot = this.node.getOwnerTree();
            var dd = ot.enableDD || ot.enableDrag || ot.enableDrop;
            if(dd && (!this.node.isRoot || ot.rootVisible)){
                Ext.dd.Registry.register(this.elNode, {
                    node: this.node,
                    handles: this.getDDHandles(),
                    isHandle: false
                });
            }
        },

        // private
        getDDHandles : function(){
            return [this.iconNode, this.textNode, this.elNode];
        },

    /**
     * Hides this node.
     */
        hide : function(){
            this.node.hidden = true;
            if(this.wrap){
                this.wrap.style.display = "none";
            }
        },

    /**
     * Shows this node.
     */
        show : function(){
            this.node.hidden = false;
            if(this.wrap){
                this.wrap.style.display = "";
            }
        },

        // private
        onContextMenu : function(e){
            if (this.node.hasListener("contextmenu") || this.node.getOwnerTree().hasListener("contextmenu")) {
                e.preventDefault();
                this.focus();
                this.fireEvent("contextmenu", this.node, e);
            }
        },

        // private
        onClick : function(e){
            if(this.dropping){
                e.stopEvent();
                return;
            }
            if(this.fireEvent("beforeclick", this.node, e) !== false){
                var a = e.getTarget('a');
                if(!this.disabled && this.node.attributes.href && a){
                    this.fireEvent("click", this.node, e);
                    return;
                }else if(a && e.ctrlKey){
                    e.stopEvent();
                }
                e.preventDefault();
                if(this.disabled){
                    return;
                }

                if(this.node.attributes.singleClickExpand && !this.animating && this.node.isExpandable()){
                    this.node.toggle();
                }

                this.fireEvent("click", this.node, e);
            }else{
                e.stopEvent();
            }
        },

        // private
        onDblClick : function(e){
            e.preventDefault();
            if(this.disabled){
                return;
            }
            if(this.fireEvent("beforedblclick", this.node, e) !== false){
                if(this.checkbox){
                    this.toggleCheck();
                }
                if(!this.animating && this.node.isExpandable()){
                    this.node.toggle();
                }
                this.fireEvent("dblclick", this.node, e);
            }
        },

        onOver : function(e){
            this.addClass('x-tree-node-over');
        },

        onOut : function(e){
            this.removeClass('x-tree-node-over');
        },

        // private
        onCheckChange : function(){
            var checked = this.checkbox.checked;
            // fix for IE6
            this.checkbox.defaultChecked = checked;
            this.node.attributes.checked = checked;
            this.fireEvent('checkchange', this.node, checked);
        },

        // private
        ecClick : function(e){
            if(!this.animating && this.node.isExpandable()){
                this.node.toggle();
            }
        },

        // private
        startDrop : function(){
            this.dropping = true;
        },

        // delayed drop so the click event doesn't get fired on a drop
        endDrop : function(){
           setTimeout(function(){
               this.dropping = false;
           }.createDelegate(this), 50);
        },

        // private
        expand : function(){
            this.updateExpandIcon();
            this.ctNode.style.display = "";
        },

        // private
        focus : function(){
            if(!this.node.preventHScroll){
                try{this.anchor.focus();
                }catch(e){}
            }else{
                try{
                    var noscroll = this.node.getOwnerTree().getTreeEl().dom;
                    var l = noscroll.scrollLeft;
                    this.anchor.focus();
                    noscroll.scrollLeft = l;
                }catch(e){}
            }
        },

    /**
     * Sets the checked status of the tree node to the passed value, or, if no value was passed,
     * toggles the checked status. If the node was rendered with no checkbox, this has no effect.
     * @param {Boolean} value (optional) The new checked status.
     */
        toggleCheck : function(value){
            var cb = this.checkbox;
            if(cb){
                cb.checked = (value === undefined ? !cb.checked : value);
                this.onCheckChange();
            }
        },

        // private
        blur : function(){
            try{
                this.anchor.blur();
            }catch(e){}
        },

        // private
        animExpand : function(callback){
            var ct = Ext.get(this.ctNode);
            ct.stopFx();
            if(!this.node.isExpandable()){
                this.updateExpandIcon();
                this.ctNode.style.display = "";
                Ext.callback(callback);
                return;
            }
            this.animating = true;
            this.updateExpandIcon();

            ct.slideIn('t', {
               callback : function(){
                   this.animating = false;
                   Ext.callback(callback);
                },
                scope: this,
                duration: this.node.ownerTree.duration || .25
            });
        },

        // private
        highlight : function(){
            var tree = this.node.getOwnerTree();
            Ext.fly(this.wrap).highlight(
                tree.hlColor || "C3DAF9",
                {endColor: tree.hlBaseColor}
            );
        },

        // private
        collapse : function(){
            this.updateExpandIcon();
            this.ctNode.style.display = "none";
        },

        // private
        animCollapse : function(callback){
            var ct = Ext.get(this.ctNode);
            ct.enableDisplayMode('block');
            ct.stopFx();

            this.animating = true;
            this.updateExpandIcon();

            ct.slideOut('t', {
                callback : function(){
                   this.animating = false;
                   Ext.callback(callback);
                },
                scope: this,
                duration: this.node.ownerTree.duration || .25
            });
        },

        // private
        getContainer : function(){
            return this.ctNode;
        },

    /**
     * Returns the element which encapsulates this node.
     * @return {HtmlElement} The DOM element. The default implementation uses a <code>&lt;li></code>.
     */
        getEl : function(){
            return this.wrap;
        },

        // private
        appendDDGhost : function(ghostNode){
            ghostNode.appendChild(this.elNode.cloneNode(true));
        },

        // private
        getDDRepairXY : function(){
            return Ext.lib.Dom.getXY(this.iconNode);
        },

        // private
        onRender : function(){
            this.render();
        },

        // private
        render : function(bulkRender){
            var n = this.node, a = n.attributes;
            var targetNode = n.parentNode ?
                  n.parentNode.ui.getContainer() : n.ownerTree.innerCt.dom;

            if(!this.rendered){
                this.rendered = true;

                this.renderElements(n, a, targetNode, bulkRender);

                if(a.qtip){
                    this.onTipChange(n, a.qtip, a.qtipTitle);
                }else if(a.qtipCfg){
                    a.qtipCfg.target = Ext.id(this.textNode);
                    Ext.QuickTips.register(a.qtipCfg);
                }
                this.initEvents();
                if(!this.node.expanded){
                    this.updateExpandIcon(true);
                }
            }else{
                if(bulkRender === true) {
                    targetNode.appendChild(this.wrap);
                }
            }
        },

        // private
        renderElements : function(n, a, targetNode, bulkRender){
            // add some indent caching, this helps performance when rendering a large tree
            this.indentMarkup = n.parentNode ? n.parentNode.ui.getChildIndent() : '';

            var cb = Ext.isBoolean(a.checked),
                nel,
                href = this.getHref(a.href),
                buf = ['<li class="x-tree-node"><div ext:tree-node-id="',n.id,'" class="x-tree-node-el x-tree-node-leaf x-unselectable ', a.cls,'" unselectable="on">',
                '<span class="x-tree-node-indent">',this.indentMarkup,"</span>",
                '<img alt="" src="', this.emptyIcon, '" class="x-tree-ec-icon x-tree-elbow" />',
                '<img alt="" src="', a.icon || this.emptyIcon, '" class="x-tree-node-icon',(a.icon ? " x-tree-node-inline-icon" : ""),(a.iconCls ? " "+a.iconCls : ""),'" unselectable="on" />',
                cb ? ('<input class="x-tree-node-cb" type="checkbox" ' + (a.checked ? 'checked="checked" />' : '/>')) : '',
                '<a hidefocus="on" class="x-tree-node-anchor" href="',href,'" tabIndex="1" ',
                 a.hrefTarget ? ' target="'+a.hrefTarget+'"' : "", '><span unselectable="on">',n.text,"</span></a></div>",
                '<ul class="x-tree-node-ct" style="display:none;"></ul>',
                "</li>"].join('');

            if(bulkRender !== true && n.nextSibling && (nel = n.nextSibling.ui.getEl())){
                this.wrap = Ext.DomHelper.insertHtml("beforeBegin", nel, buf);
            }else{
                this.wrap = Ext.DomHelper.insertHtml("beforeEnd", targetNode, buf);
            }

            this.elNode = this.wrap.childNodes[0];
            this.ctNode = this.wrap.childNodes[1];
            var cs = this.elNode.childNodes;
            this.indentNode = cs[0];
            this.ecNode = cs[1];
            this.iconNode = cs[2];
            var index = 3;
            if(cb){
                this.checkbox = cs[3];
                // fix for IE6
                this.checkbox.defaultChecked = this.checkbox.checked;
                index++;
            }
            this.anchor = cs[index];
            this.textNode = cs[index].firstChild;
        },

        /**
         * @private Gets a normalized href for the node.
         * @param {String} href
         */
        getHref : function(href){
            return Ext.isEmpty(href) ? (Ext.isGecko ? '' : '#') : href;
        },

    /**
     * Returns the &lt;a> element that provides focus for the node's UI.
     * @return {HtmlElement} The DOM anchor element.
     */
        getAnchor : function(){
            return this.anchor;
        },

    /**
     * Returns the text node.
     * @return {HtmlNode} The DOM text node.
     */
        getTextEl : function(){
            return this.textNode;
        },

    /**
     * Returns the icon &lt;img> element.
     * @return {HtmlElement} The DOM image element.
     */
        getIconEl : function(){
            return this.iconNode;
        },

    /**
     * Returns the checked status of the node. If the node was rendered with no
     * checkbox, it returns false.
     * @return {Boolean} The checked flag.
     */
        isChecked : function(){
            return this.checkbox ? this.checkbox.checked : false;
        },

        // private
        updateExpandIcon : function(){
            if(this.rendered){
                var n = this.node,
                    c1,
                    c2,
                    cls = n.isLast() ? "x-tree-elbow-end" : "x-tree-elbow",
                    hasChild = n.hasChildNodes();
                if(hasChild || n.attributes.expandable){
                    if(n.expanded){
                        cls += "-minus";
                        c1 = "x-tree-node-collapsed";
                        c2 = "x-tree-node-expanded";
                    }else{
                        cls += "-plus";
                        c1 = "x-tree-node-expanded";
                        c2 = "x-tree-node-collapsed";
                    }
                    if(this.wasLeaf){
                        this.removeClass("x-tree-node-leaf");
                        this.wasLeaf = false;
                    }
                    if(this.c1 != c1 || this.c2 != c2){
                        Ext.fly(this.elNode).replaceClass(c1, c2);
                        this.c1 = c1; this.c2 = c2;
                    }
                }else{
                    if(!this.wasLeaf){
                        Ext.fly(this.elNode).replaceClass("x-tree-node-expanded", "x-tree-node-collapsed");
                        delete this.c1;
                        delete this.c2;
                        this.wasLeaf = true;
                    }
                }
                var ecc = "x-tree-ec-icon "+cls;
                if(this.ecc != ecc){
                    this.ecNode.className = ecc;
                    this.ecc = ecc;
                }
            }
        },

        // private
        onIdChange: function(id){
            if(this.rendered){
                this.elNode.setAttribute('ext:tree-node-id', id);
            }
        },

        // private
        getChildIndent : function(){
            if(!this.childIndent){
                var buf = [],
                    p = this.node;
                while(p){
                    if(!p.isRoot || (p.isRoot && p.ownerTree.rootVisible)){
                        if(!p.isLast()) {
                            buf.unshift('<img alt="" src="'+this.emptyIcon+'" class="x-tree-elbow-line" />');
                        } else {
                            buf.unshift('<img alt="" src="'+this.emptyIcon+'" class="x-tree-icon" />');
                        }
                    }
                    p = p.parentNode;
                }
                this.childIndent = buf.join("");
            }
            return this.childIndent;
        },

        // private
        renderIndent : function(){
            if(this.rendered){
                var indent = "",
                    p = this.node.parentNode;
                if(p){
                    indent = p.ui.getChildIndent();
                }
                if(this.indentMarkup != indent){ // don't rerender if not required
                    this.indentNode.innerHTML = indent;
                    this.indentMarkup = indent;
                }
                this.updateExpandIcon();
            }
        },

        destroy : function(){
            if(this.elNode){
                Ext.dd.Registry.unregister(this.elNode.id);
            }

            Ext.each(['textnode', 'anchor', 'checkbox', 'indentNode', 'ecNode', 'iconNode', 'elNode', 'ctNode', 'wrap', 'holder'], function(el){
                if(this[el]){
                    Ext.fly(this[el]).remove();
                    delete this[el];
                }
            }, this);
            delete this.node;
        }
    });

    /**
     * @class Ext.tree.RootTreeNodeUI
     * This class provides the default UI implementation for <b>root</b> Ext TreeNodes.
     * The RootTreeNode UI implementation allows customizing the appearance of the root tree node.<br>
     * <p>
     * If you are customizing the Tree's user interface, you
     * may need to extend this class, but you should never need to instantiate this class.<br>
     */
    Ext.tree.RootTreeNodeUI = Ext.extend(Ext.tree.TreeNodeUI, {
        // private
        render : function(){
            if(!this.rendered){
                var targetNode = this.node.ownerTree.innerCt.dom;
                this.node.expanded = true;
                targetNode.innerHTML = '<div class="x-tree-root-node"></div>';
                this.wrap = this.ctNode = targetNode.firstChild;
            }
        },
        collapse : Ext.emptyFn,
        expand : Ext.emptyFn
    });