public IEnvironmentVariableFilePath GetChildFilePath(string fileName)
            {
                Argument.IsNotNullOrEmpty(nameof(fileName), fileName);

                var pathString = PathBrowsingHelpers.GetChildFilePath(this, fileName);

                //Debug.Assert(pathString.IsValidEnvVarFilePath());

                return(new EnvironmentVariableFilePath(pathString));
            }
            public IAbsoluteFilePath GetChildFilePath(string fileName)
            {
                Argument.IsNotNullOrEmpty(nameof(fileName), fileName);

                var pathString = PathBrowsingHelpers.GetChildFilePath(this, fileName);

                //Debug.Assert(pathString.IsValidAbsoluteFilePath());

                return(new AbsoluteFilePath(pathString));
            }