anchor.diff:  (defun buffer-insert-char (buffer linum col c)
     (buffer-read-only-guard buffer buffer-insert-char)
     (setf (buffer-modified-p buffer) t)
  +  (when (and (= linum (buffer-mark-linum buffer))
  +             (<= col (buffer-mark-col buffer)))
  +    (incf (buffer-mark-col buffer)))
     (if (char= c #\newline)
       (buffer-insert-newline buffer linum col)
       (let ((line (buffer-get-line buffer linum)))
  
positive.code: (defun buffer-insert-newline (buffer linum col)
    (buffer-read-only-guard buffer buffer-insert-newline)
    (setf (buffer-modified-p buffer) t)
    (let ((line (buffer-get-line buffer linum)))
      (let ((newline
              (make-line line
  
negative.code:   tail-line
    cache-line
    cache-linum
    (mark-linum 1)
    (mark-col 0)
    keep-binfo
    (nlines 1))
  
  