anchor.diff:      :initarg :impl
       :initform nil
       :accessor virtual-frame-impl
  -    :type lem:implementation)
  +    :type implementation)
      (id/frame-table
       :initarg :id/frame-table
       :accessor virtual-frame-id/frame-table
  
positive.code:               (start-pos (point-charpos p)))
            (insert-button p
                           ;; virtual frame name on header
                           (let* ((buffer (window-buffer (lem:frame-current-window frame)))
                                  (name (buffer-name buffer)))
                             (format nil "~a~a:~a "
                                     (if focusp #\# #\space)
  
negative.code:          (frame (search-next-frame vf (virtual-frame-current vf))))
      (when frame
        (setf (virtual-frame-current vf) frame)
        (map-frame (implementation) frame))
      (lem::change-display-size-hook)
      (setf (virtual-frame-changed vf) t)))
  
  