anchor.diff:  (defgeneric insert-char/point (point char)
     (:method (point char)
       (with-modify-buffer (point-buffer point)
  -      (check-read-only-at-point (point-line point) (point-charpos point) 0)
  +      (check-read-only-at-point point 0)
         (cond
           ((char= char #\newline)
            (%insert-newline/point (point-buffer point)
  
positive.code:       char)))
  
  (defun %insert-line-string/point (line charpos string)
    (check-read-only-at-point line charpos 0)
    (shift-sticky-objects line charpos (length string))
    (setf (line-str line)
          (concatenate 'string
  
negative.code:   (:method (point string)
      (let ((buffer (point-buffer point)))
        (with-modify-buffer buffer
          (check-read-only-at-point point 0)
          (loop :with start := 0
                :for pos := (position #\newline string :start start)
                :for line := (point-line point) :then (line-next line)
  