-Some historic curses implementations had, as an undocumented feature, the
-ability to do the equivalent of \fBclearok(..., 1)\fR by saying
-\fBtouchwin(stdscr)\fR or \fBclear(stdscr)\fR. This will not work under
-ncurses.
+These functions were introduced by SVr4.
+The Solaris curses header file,
+for instance, defines both an actual function and macro for each.
+The macros give the same result as the actual functions.
+SVr4 curses does not check the window parameter \fIwin\fP to ensure
+that it is not \fBNULL\fP;
+otherwise this implementation behaves the same as SVr4.
+.PP
+The XSI Curses standard, Issue 4 describes these functions,
+but defines no error conditions.