The source code

    /*!
     * Ext JS Library 3.4.0
     * Copyright(c) 2006-2011 Sencha Inc.
     * licensing@sencha.com
     * http://www.sencha.com/license
     */
    /**
     * @class Ext.Element
     */
    Ext.Element.addMethods(
    function() {
    	var GETDOM = Ext.getDom,
    		GET = Ext.get,
    		DH = Ext.DomHelper;

    	return {
    	    /**
    	     * Appends the passed element(s) to this element
    	     * @param {String/HTMLElement/Array/Element/CompositeElement} el
    	     * @return {Ext.Element} this
    	     */
    	    appendChild: function(el){
    	        return GET(el).appendTo(this);
    	    },

    	    /**
    	     * Appends this element to the passed element
    	     * @param {Mixed} el The new parent element
    	     * @return {Ext.Element} this
    	     */
    	    appendTo: function(el){
    	        GETDOM(el).appendChild(this.dom);
    	        return this;
    	    },

    	    /**
    	     * Inserts this element before the passed element in the DOM
    	     * @param {Mixed} el The element before which this element will be inserted
    	     * @return {Ext.Element} this
    	     */
    	    insertBefore: function(el){
    	        (el = GETDOM(el)).parentNode.insertBefore(this.dom, el);
    	        return this;
    	    },

    	    /**
    	     * Inserts this element after the passed element in the DOM
    	     * @param {Mixed} el The element to insert after
    	     * @return {Ext.Element} this
    	     */
    	    insertAfter: function(el){
    	        (el = GETDOM(el)).parentNode.insertBefore(this.dom, el.nextSibling);
    	        return this;
    	    },

    	    /**
    	     * Inserts (or creates) an element (or DomHelper config) as the first child of this element
    	     * @param {Mixed/Object} el The id or element to insert or a DomHelper config to create and insert
    	     * @return {Ext.Element} The new child
    	     */
    	    insertFirst: function(el, returnDom){
                el = el || {};
                if(el.nodeType || el.dom || typeof el == 'string'){ // element
                    el = GETDOM(el);
                    this.dom.insertBefore(el, this.dom.firstChild);
                    return !returnDom ? GET(el) : el;
                }else{ // dh config
                    return this.createChild(el, this.dom.firstChild, returnDom);
                }
            },

    	    /**
    	     * Replaces the passed element with this element
    	     * @param {Mixed} el The element to replace
    	     * @return {Ext.Element} this
    	     */
    	    replace: function(el){
    	        el = GET(el);
    	        this.insertBefore(el);
    	        el.remove();
    	        return this;
    	    },

    	    /**
    	     * Replaces this element with the passed element
    	     * @param {Mixed/Object} el The new element or a DomHelper config of an element to create
    	     * @return {Ext.Element} this
    	     */
    	    replaceWith: function(el){
    		    var me = this;

                if(el.nodeType || el.dom || typeof el == 'string'){
                    el = GETDOM(el);
                    me.dom.parentNode.insertBefore(el, me.dom);
                }else{
                    el = DH.insertBefore(me.dom, el);
                }

    	        delete Ext.elCache[me.id];
    	        Ext.removeNode(me.dom);
    	        me.id = Ext.id(me.dom = el);
    	        Ext.Element.addToCache(me.isFlyweight ? new Ext.Element(me.dom) : me);
                return me;
    	    },

    		/**
    		 * Creates the passed DomHelper config and appends it to this element or optionally inserts it before the passed child element.
    		 * @param {Object} config DomHelper element config object.  If no tag is specified (e.g., {tag:'input'}) then a div will be
    		 * automatically generated with the specified attributes.
    		 * @param {HTMLElement} insertBefore (optional) a child element of this element
    		 * @param {Boolean} returnDom (optional) true to return the dom node instead of creating an Element
    		 * @return {Ext.Element} The new child element
    		 */
    		createChild: function(config, insertBefore, returnDom){
    		    config = config || {tag:'div'};
    		    return insertBefore ?
    		    	   DH.insertBefore(insertBefore, config, returnDom !== true) :
    		    	   DH[!this.dom.firstChild ? 'overwrite' : 'append'](this.dom, config,  returnDom !== true);
    		},

    		/**
    		 * Creates and wraps this element with another element
    		 * @param {Object} config (optional) DomHelper element config object for the wrapper element or null for an empty div
    		 * @param {Boolean} returnDom (optional) True to return the raw DOM element instead of Ext.Element
    		 * @return {HTMLElement/Element} The newly created wrapper element
    		 */
    		wrap: function(config, returnDom){
    		    var newEl = DH.insertBefore(this.dom, config || {tag: "div"}, !returnDom);
    		    newEl.dom ? newEl.dom.appendChild(this.dom) : newEl.appendChild(this.dom);
    		    return newEl;
    		},

    		/**
    		 * Inserts an html fragment into this element
    		 * @param {String} where Where to insert the html in relation to this element - beforeBegin, afterBegin, beforeEnd, afterEnd.
    		 * @param {String} html The HTML fragment
    		 * @param {Boolean} returnEl (optional) True to return an Ext.Element (defaults to false)
    		 * @return {HTMLElement/Ext.Element} The inserted node (or nearest related if more than 1 inserted)
    		 */
    		insertHtml : function(where, html, returnEl){
    		    var el = DH.insertHtml(where, this.dom, html);
    		    return returnEl ? Ext.get(el) : el;
    		}
    	};
    }());