private static string BuildLink(MarkupRendererContext context, string content, string url, string anchor)
        {
            var builder = new StringBuilder();
            builder.Append("<a href='");

            if (url != null) builder.Append(context.ResolveInterContentLink(url));
            else builder.Append(context.ResolveInterContentLink(content));

            if (anchor != null) builder.Append("#" + anchor);

            builder.Append("'>");
            builder.Append(HttpUtility.HtmlEncode(content));
            builder.Append("</a>");
            return builder.ToString();
        }