anchor.diff:  (defun start-line-p ()
     (<= (current-linum) 1))
   
  -(defun tail-line-p ()
  +(defun end-line-p ()
     (<= (buffer-nlines (current-buffer))
         (current-linum)))
   
  
positive.code: 
  (defun blank-line-p ()
    (let ((string (current-line-string))
          (eof-p (tail-line-p)))
      (when (string= "" (string-trim '(#\space #\tab) string))
        (+ (length string)
           (if eof-p 0 1)))))
  
negative.code:   (beginning-of-line)
    (if (plusp n)
        (dotimes (_ n t)
          (when (end-line-p)
            (end-of-line)
            (return))
          (incf (current-linum)))
  