void FindFiles(string directoryPath, List <string> files)
        {
            files.AddRange(FileEx.FindFiles(directoryPath, "*.source.md"));

            foreach (var subDirectory in Directory.EnumerateDirectories(directoryPath)
                     .Where(IncludeDirectory))
            {
                FindFiles(subDirectory, files);
            }
        }
        void FindFiles(string directoryPath, List <string> files)
        {
            IEnumerable <string> findFiles;

            if (convention == DocumentConvention.SourceTransform)
            {
                findFiles = FileEx.FindFiles(directoryPath, "*.source.md");
            }
            else
            {
                findFiles = FileEx.FindFiles(directoryPath, "*.md")
                            .Where(x => !x.Contains(".include."));
            }

            files.AddRange(findFiles);

            foreach (var subDirectory in Directory.EnumerateDirectories(directoryPath)
                     .Where(IncludeDirectory))
            {
                FindFiles(subDirectory, files);
            }
        }