+.PP
+The menu facility was documented in SVr4.2 in
+\fICharacter User Interface Programming (UNIX SVR4.2)\fP.
+.PP
+It is not part of X/Open Curses.
+.PP
+Aside from ncurses, there are few implementations:
+.bP
+systems based on SVr4 source code, e.g., Solaris.
+.bP
+NetBSD curses.
+.PP
+A few functions in this implementation are extensions added for ncurses,
+but not provided by other implementations, e.g.,
+\fBform_driver_w\fP,
+\fBunfocus_current_field\fP.