when mixed newlines are found in a file, can the newlines attribute be a list of those that are found, instead of "mixed"?
shouldn't open() mode "wU" also be illegal?
- Why isn't "rU+" allowed? It's understandable that "+" is not allowed for output, but I can't see a good reason why it shouldn't be allowed to open file for read/write, and read with universal support (maybe some implementation detail?). Allowing this would even easy the task, since when writting to the file the programmer could consider the newlines attribute, if he wants.