How to force display-buffer-in-side-window to open side window on right?

[Jean Louis <bugs@gnu.support>]

I am trying to make function to provide 2 buffers in 2 windows, side
by side.

(defun rcd-two-windows (buffer-left buffer-right &optional window-register)
  "Display BUFFER-LEFT and BUFFER-RIGHT only.

Previous window configuration is saved register ?r or to optional
WINDOW-REGISTER.

Parent function may restore window configuration by using the
function `jump-to-register' with WINDOW-REGISTER as argument."
  (cond ((and (buffer-live-p buffer-left) (buffer-live-p buffer-right))
	 (let ((register (or window-register ?r)))
	   (window-configuration-to-register register)
	   (switch-to-buffer buffer-left)
	   (delete-other-windows)
	   (display-buffer-in-side-window buffer-right '(side right))))
	(t (user-error "Buffers `%s' and `%s' must be live" buffer-left buffer-right))))


However, with `emacs -Q' this below gives me window and smaller window
down on the bottom instead on right side

(let ((buffer-left (get-buffer-create "*My Left*"))
      (buffer-right (get-buffer-create "*My Right*")))
  (rcd-two-windows buffer-left buffer-right))

What am I doing wrong?


--
Jean

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