Draw a border around the edges of the window.
ls
Left side.
rs
Right side.
ts
Top side.
bs
Bottom side.
tl
Upper-left corner.
tr
Upper-right corner.
bl
Bottom-left corner.
br
Bottom-right corner.
Each parameter specifies the character to use for a specific part of
the border. The characters can be specified as integers or as
one-character strings. A 0 value for any parameter will cause the
default character to be used for that parameter.