anchor.diff:      (clear)
       (refresh)
       (getch)
  -
  -    (endwin)))
  +    (endwin)))
  
positive.code: 
  ;; 190302
  (defun nctest5 ()
    (let ((scr (initscr)))
      (addstr (format nil "~A~%" "no background "))
      (wgetch scr)
  
negative.code:     ;; (erase) and (clear) use the last bkgd char to overwrite the window.
      (clear)
      (getch)
  
      ;; here we only set a color as the bg char, the default bg char is space
      (bkgdset (color-pair 2))
      (addstr (format nil "bkgdset: green on white~%"))
      (getch)
  
      ;; the default color pair is black on white
      (bkgd (color-pair 0))
      (addstr (format nil "bkgd: default colors~%"))
      (getch)
  