%F=chv

With this terminal command, you can define the characters to be used in the frame of a window.

c	The first character will be used for the four corners of the window frame.
h	The second character will be used for the horizontal frame lines (top and bottom frame lines).
v	The third character will be used for the vertical frame lines (left and right frame lines).

Example: The command %F=+-! would cause the window frame to look like this:

+------------------------+
!                        !
!                        !
!                        !
!                        !
+------------------------+

For further information on window processing, see the DEFINE WINDOW statement (in the Statements documentation).