+.PP
+Functions using a window parameter return an error if it is null.
+.RS
+.TP 5
+\fBwgetn_wstr\fP
+returns an error if the associated call to \fBwget_wch\fP failed.
+.RE
+.PP
+Functions with a "mv" prefix first perform a cursor movement using
+\fBwmove\fP, and return an error if the position is outside the window,
+or if the window pointer is null.