Re: Bug in format-time-string in emacs 21.1?

[Richard Stallman]

    Alternatively, we could introduce more conditional blocks to
    strftime.c to do something sensible with the POSIX.2 extensions on
    platforms that only support POSIX.1 formats.  I think most of them
    could be handled without too much effort.

If someone wants to do this work, it would clearly give a better
result than documenting flaws.