anchor.diff:    "Move the reading line cursor down. If scrolling off screen, move
   the screen as well."
     (pflet ((cursor-down ()
  -    (let ((original-position 
  +    (let ((original-position
               (ps:chain (parse-int
                          (ps:@ (ps:chain document (query-selector "#reading-line-cursor")) style top) 10))))
         (setf (ps:@ (ps:chain document (query-selector "#reading-line-cursor")) style top)
  
positive.code:   "Move the reading line cursor up. If scrolling off screen, move the
  screen as well."
    (pflet ((cursor-up ()
      (let ((original-position 
              (ps:chain (parse-int
                         (ps:@ (ps:chain document (query-selector "#reading-line-cursor")) style top) 10))))
        (setf (ps:@ (ps:chain document (query-selector "#reading-line-cursor")) style top)
  
negative.code:   (let* ((content (markup:markup
                     (:style (style mode))
                     (:span :id "reading-line-cursor" "")))
           (insert-content (ps:ps
                             (ps:chain document body (|insertAdjacentHTML| "afterbegin" (ps:lisp content)))
                             (setf (ps:@ (ps:chain document (query-selector "#reading-line-cursor")) style top) "10px"))))
      (ffi-buffer-evaluate-javascript (buffer mode) insert-content)))
  