Attached is a patch that adds documentation for a few things that have existed in subprocess for a while without documentation. The "startupinfo" parameter takes subprocess.STARTUPINFO object which takes a few different options for its attributes, but none of this was documented. The "creationflags" parameter takes subprocess.CREATE_NEW_WINDOW or subprocess.CREATE_NEW_PROCESS_GROUP, but neither were documented as options or what the options mean.
You can indent the "attribute" directives and avoid to repeat "STARTUPINFO." before every attribute. If STD_INPUT_HANDLE and the other constants are attributes of STARTUPINFO they should be indented too, otherwise a line that says that subprocess also provides those at module level might be better. Another short note at the beginning of the section that mentions that this class/attributes are available on Windows only would be good too. There's also some trailing whitespace that should be removed.
