System.Xml.XmlElementList.NextElemInPreOrder C# (CSharp) Méthode

        private XmlNode NextElemInPreOrder( XmlNode curNode ) {
            Debug.Assert( curNode != null );
            //For preorder walking, first try its child
            XmlNode retNode = curNode.FirstChild;
            if ( retNode == null ) {
                //if no child, the next node forward will the be the NextSibling of the first ancestor which has NextSibling
                //so, first while-loop find out such an ancestor (until no more ancestor or the ancestor is the rootNode
                retNode = curNode;
                while ( retNode != null 
                        && retNode != rootNode 
                        && retNode.NextSibling == null ) {
                    retNode = retNode.ParentNode;
                }
                //then if such ancestor exists, set the retNode to its NextSibling
                if ( retNode != null && retNode != rootNode )
                    retNode = retNode.NextSibling;
            }
            if ( retNode == this.rootNode ) 
                retNode = null;
            return retNode;
        }