The source code

    /**
     * @class Ext.DomHelper
     */
    Ext.apply(Ext.DomHelper,
    function(){
        var pub,
            afterbegin = 'afterbegin',
            afterend = 'afterend',
            beforebegin = 'beforebegin',
            beforeend = 'beforeend',
            confRe = /tag|children|cn|html$/i;

        // private
        function doInsert(el, o, returnElement, pos, sibling, append){
            el = Ext.getDom(el);
            var newNode;
            if (pub.useDom) {
                newNode = createDom(o, null);
                if (append) {
                    el.appendChild(newNode);
                } else {
                    (sibling == 'firstChild' ? el : el.parentNode).insertBefore(newNode, el[sibling] || el);
                }
            } else {
                newNode = Ext.DomHelper.insertHtml(pos, el, Ext.DomHelper.createHtml(o));
            }
            return returnElement ? Ext.get(newNode, true) : newNode;
        }

        // build as dom
        /** @ignore */
        function createDom(o, parentNode){
            var el,
                doc = document,
                useSet,
                attr,
                val,
                cn;

            if (Ext.isArray(o)) {                       // Allow Arrays of siblings to be inserted
                el = doc.createDocumentFragment(); // in one shot using a DocumentFragment
                for (var i = 0, l = o.length; i < l; i++) {
                    createDom(o[i], el);
                }
            } else if (typeof o == 'string') {         // Allow a string as a child spec.
                el = doc.createTextNode(o);
            } else {
                el = doc.createElement( o.tag || 'div' );
                useSet = !!el.setAttribute; // In IE some elements don't have setAttribute
                for (var attr in o) {
                    if(!confRe.test(attr)){
                        val = o[attr];
                        if(attr == 'cls'){
                            el.className = val;
                        }else{
                            if(useSet){
                                el.setAttribute(attr, val);
                            }else{
                                el[attr] = val;
                            }
                        }
                    }
                }
                Ext.DomHelper.applyStyles(el, o.style);

                if ((cn = o.children || o.cn)) {
                    createDom(cn, el);
                } else if (o.html) {
                    el.innerHTML = o.html;
                }
            }
            if(parentNode){
               parentNode.appendChild(el);
            }
            return el;
        }

        pub = {
            /**
             * Creates a new Ext.Template from the DOM object spec.
             * @param {Object} o The DOM object spec (and children)
             * @return {Ext.Template} The new template
             */
            createTemplate : function(o){
                var html = Ext.DomHelper.createHtml(o);
                return new Ext.Template(html);
            },

            /** True to force the use of DOM instead of html fragments @type Boolean */
            useDom : false,

            /**
             * Creates new DOM element(s) and inserts them before el.
             * @param {Mixed} el The context element
             * @param {Object/String} o The DOM object spec (and children) or raw HTML blob
             * @param {Boolean} returnElement (optional) true to return a Ext.Element
             * @return {HTMLElement/Ext.Element} The new node
             * @hide (repeat)
             */
            insertBefore : function(el, o, returnElement){
                return doInsert(el, o, returnElement, beforebegin);
            },

            /**
             * Creates new DOM element(s) and inserts them after el.
             * @param {Mixed} el The context element
             * @param {Object} o The DOM object spec (and children)
             * @param {Boolean} returnElement (optional) true to return a Ext.Element
             * @return {HTMLElement/Ext.Element} The new node
             * @hide (repeat)
             */
            insertAfter : function(el, o, returnElement){
                return doInsert(el, o, returnElement, afterend, 'nextSibling');
            },

            /**
             * Creates new DOM element(s) and inserts them as the first child of el.
             * @param {Mixed} el The context element
             * @param {Object/String} o The DOM object spec (and children) or raw HTML blob
             * @param {Boolean} returnElement (optional) true to return a Ext.Element
             * @return {HTMLElement/Ext.Element} The new node
             * @hide (repeat)
             */
            insertFirst : function(el, o, returnElement){
                return doInsert(el, o, returnElement, afterbegin, 'firstChild');
            },

            /**
             * Creates new DOM element(s) and appends them to el.
             * @param {Mixed} el The context element
             * @param {Object/String} o The DOM object spec (and children) or raw HTML blob
             * @param {Boolean} returnElement (optional) true to return a Ext.Element
             * @return {HTMLElement/Ext.Element} The new node
             * @hide (repeat)
             */
            append: function(el, o, returnElement){
                return doInsert(el, o, returnElement, beforeend, '', true);
            },

            /**
             * Creates new DOM element(s) without inserting them to the document.
             * @param {Object/String} o The DOM object spec (and children) or raw HTML blob
             * @return {HTMLElement} The new uninserted node
             */
            createDom: createDom
        };
        return pub;
    }());