-.SH PORTABILITY
-The XSI Curses standard, Issue 4 describes these functions.
-
-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.
+.PP
+X/Open Curses does not specify any error conditions.
+In this implementation
+.RS 3
+.TP 5
+\fBis_linetouched\fP
+returns
+.B ERR
+if the window pointer is null, or
+if the line number is outside the window boundaries.
+.IP
+The constant \fBERR\fP is distinct from \fBTRUE\fP and \fBFALSE\fP,
+which are the normal return values of this function.
+Because the function returns a \fBbool\fP,
+returning \fBERR\fP (which is neither \fBTRUE\fP nor \fBFALSE\fP)
+may not be supported by the compiler.
+.IP
+To provide error-checking and also match the X/Open function prototype,
+the \fBERR\fP is provided by a macro named \fB\%is_linetouched\fP.
+The actual function returns \fBFALSE\fP when it detects an error.
+.TP 5
+\fBwtouchln\fP
+returns
+.B ERR
+if the window pointer is null, or
+if the line number is outside the window boundaries.
+.RE