+.PP
+X/Open defines no error conditions.
+In this implementation
+.TP 5
+\fBdelwin\fR
+returns an error if the window pointer is null, or
+if the window is the parent of another window.
+.TP 5
+\fBderwin\fP
+returns an error if the parent window pointer is null, or
+if any of its ordinates or dimensions is negative, or
+if the resulting window does not fit inside the parent window.
+.TP 5
+\fBdupwin\fP
+returns an error if the window pointer is null.
+.IP
+This implementation also maintains a list of windows,
+and checks that the pointer passed to \fBdelwin\fP is one that
+it created, returning an error if it was not..
+.TP 5
+\fBmvderwin\fP
+returns an error
+if the window pointer is null, or
+if some part of the window would be placed off-screen.
+.TP 5
+\fBmvwin\fP
+returns an error
+if the window pointer is null, or
+if the window is really a pad, or
+if some part of the window would be placed off-screen.
+.TP 5
+\fBnewwin\fP
+will fail if either of its beginning ordinates is negative, or
+if either the number of lines or columns is negative.
+.TP 5
+\fBsyncok\fP
+returns an error
+if the window pointer is null.
+.TP 5
+\fBsubwin\fP
+returns an error if the parent window pointer is null, or
+if any of its ordinates or dimensions is negative, or
+if the resulting window does not fit inside the parent window.
+.PP
+The functions which return a window pointer
+may also fail if there is insufficient memory for its data structures.
+Any of these functions will fail if the screen has not been initialized,
+i.e., with \fBinitscr\fP or \fBnewterm\fP.