Hello, I would like to provide some code in order to use a stack to manage the allocation of input and output streams. It is available in https://gist.github.com/4015700 . Please have a look. I think it is more efficient and clearer than the current approach in `l3file`. It is obvious that it is fairly rough. And there is still some more work to be done in `package` module in order to compatible with LaTeX2e. Best regards, -- Qing Lee