private void CreateNAVDocument(XDocument contentDocument)
        {
            var html = new XElement(WWWNamespaces.XHTML + "html");
            html.Add(new XAttribute(XNamespace.Xmlns + "epub", EPubNamespaces.OpsNamespace));
            contentDocument.Add(html);

            var head = new XElement(WWWNamespaces.XHTML + "head");
            html.Add(head);
            var meta = new XElement(WWWNamespaces.XHTML + "meta");
            meta.Add(new XAttribute("charset","utf-8"));
            head.Add(meta);
            var title = new XElement(WWWNamespaces.XHTML + "title");
            if (string.IsNullOrEmpty(PageTitle))
            {
                title.Value = "Table of Contents";
            }
            else
            {
                title.Value = WebUtility.HtmlEncode(PageTitle) + " - Table of Contents";
            }
            head.Add(title);
            foreach (var file in _styles)
            {
                var cssStyleSheet = new Link(HTMLElementType.HTML5);
                cssStyleSheet.Relation.Value = "stylesheet";
                cssStyleSheet.Type.Value = file.GetMediaType().GetAsSerializableString();
                cssStyleSheet.HRef.Value = file.PathInEPUB.GetRelativePath(NAVFilePath, FlatStructure);
                head.Add(cssStyleSheet.Generate());
            }

            var body = new XElement(WWWNamespaces.XHTML + "body");
            body.Add(new XAttribute("class","nav_body"));
            html.Add(body);

            var navElement = _documentNavigationMap.GenerateXMLMap();
            if (navElement != null)
            {
                body.Add(navElement);
            }

            var landmarksElement = _landmarks.GenerateXMLMap();
            if (landmarksElement != null)
            {
                body.Add(landmarksElement);
            }
        }