Select some code and open that code in another frame for reference.

gistfile1.el

(defun narrow-to-region-indirect (start end)
  "Restrict editing in this buffer to the current region, indirectly."
  (interactive "r")
  (let ((buf (clone-indirect-buffer nil nil)))
    (with-current-buffer buf
      (narrow-to-region start end))
    (select-frame (make-frame))
    (switch-to-buffer buf)))

(global-set-key (kbd "C-c \"") 'narrow-to-region-indirect)