public static string    librarDataRootFolder(this TMConfig tmConfig)
        {
            //set xmlDatabasePath based on virtualPathMapping
            var virtualPathMapping = tmConfig.virtualPathMapping();
            var xmlDatabasePath    = TMConfig.WebRoot.pathCombine(virtualPathMapping).fullPath();

            //check if we can write to xmlDatabasePath (and default to App_Data if we can't write to provided direct)
            if (xmlDatabasePath.canNotWriteToPath())
            {
                xmlDatabasePath = TMConfig.AppData_Folder;
            }

            return(xmlDatabasePath);
        }