C<-b>, C<-c>, C<-k>, C<-g>, C<-p>, C<-u>, C<-A> are not implemented.
(S<Mac OS>)
-C<-g>, C<-k>, C<-l>, C<-p>, C<-u>, C<-A> are not particularly meaningful.
+C<-g>, C<-k>, C<-l>, C<-u>, C<-A> are not particularly meaningful.
(Win32, VMS, S<RISC OS>)
+C<-p> is not particularly meaningful. (VMS, S<RISC OS>)
+
C<-d> is true if passed a device spec without an explicit directory.
(VMS)