anchor.diff:    (if (minusp n)
         (scroll-down (- n))
         (dotimes (_ n t)
  -        (when (and (= (window-cursor-y (current-window))
  +        (when (and (= (window-cursor-y-if-wrapping (current-window))
                         (- (window-height) 2))
                      (/= 1 (window-vtop-linum)))
             (unless (forward-line (- n))
  
positive.code:   (if (minusp n)
        (scroll-up (- n))
        (dotimes (_ n t)
          (when (= (window-cursor-y (current-window)) 0)
            (unless (forward-line n)
              (return nil)))
          (let ((prev-linum (window-vtop-linum))
  
negative.code:     (charms/ll:wattroff (window-win window)
                          attr)))
  
  (defun window-cursor-y (window)
    (- (window-current-linum window)
       (window-vtop-linum window)))
  
  (defun window-cursor-y-if-wrapping (window)
    (if (buffer-truncate-lines (window-buffer window))
        (+ (- (window-current-linum window)
              (window-vtop-linum window))
           (window-wrapping-offset window))
        (window-cursor-y window)))
  
  (defun window-print-line (window y str &key (start-x 0) (string-start 0) string-end)
    (check-type str fatstring)
  