OK, but surely providing the possibility to override the POSIX flag isn't difficult. That doesn't require any change in default behaviour. 

It also seems it should be possible to request enhancements without having to do the work myself. Can we agree that parsing Windows command lines is a generally useful thing to do? We already have a module that can parse UNIX command lines which isn't unrelated. Perhaps this should be changed to "enhancement" rather than "invalid". 

Whether or not the original author of shlex cared about Windows seems to be beside the point.