System.Xml.XmlElementList.PrevElemInPreOrder C# (CSharp) Method

        private XmlNode PrevElemInPreOrder( XmlNode curNode ) {
            Debug.Assert( curNode != null );
            //For preorder walking, the previous node will be the right-most node in the tree of PreviousSibling of the curNode
            XmlNode retNode = curNode.PreviousSibling;
            // so if the PreviousSibling is not null, going through the tree down to find the right-most node
            while ( retNode != null ) {
                if ( retNode.LastChild == null )
                    break;
                retNode = retNode.LastChild;
            }
            // if no PreviousSibling, the previous node will be the curNode's parentNode
            if ( retNode == null )
                retNode = curNode.ParentNode;
            if ( retNode == this.rootNode )
                retNode = null;
            return retNode;
        }