+.PP
+X/Open does not define any error conditions.
+In this implementation
+.RS
+.TP 5
+\fBis_linetouched\fP
+returns an error
+if the window pointer is null, or
+if the line number is outside the window.
+Note that ERR is distinct from TRUE and FALSE, which are the normal return values of this function.
+.TP 5
+\fBwtouchln\fP
+returns an error
+if the window pointer is null, or
+if the line number is outside the window.
+.RE