@code{optind} to 0. Other implementations provide @code{optreset},
causing a reset by setting it non-zero, although it does not
necessarily re-read @env{POSIXLY_CORRECT}.
+@item
+Mixing a leading @samp{-} or @samp{+} with a leading @samp{:} in the
+optstring argument has inconsistent effects across platforms.
@end itemize