anchor.diff:    (:export-class-name-p t)
     (:export-accessor-names-p t)
     (:accessor-name-transformer #'class*:name-identity)
  -  (:documentation "Node structure of the history tree."))
  +  (:documentation "Node structure of the history tree.
  +Each node has one parent (unless it's a root node) and zero or multiple
  +children.  Nodes may have zero or multiple owners."))
   
   (export 'data)
   (defmethod data ((node node))
  
positive.code:                 :documentation "Timestamp of the last access to this node by the
  owner."))
    (:accessor-name-transformer #'class*:name-identity)
    (:documentation "The relationship between an owner and one of its nodes."))
  
  (export-always 'last-access)
  (defmethod last-access ((binding binding))
  
negative.code:   (:export-class-name-p t)
    (:export-accessor-names-p t)
    (:accessor-name-transformer #'class*:name-identity)
    (:documentation "The high-level information about an owner.
  Each owner is identified by a unique identifier, which is arbitrary data (may
  even be NIL)."))
  
  (defmethod (setf current) (value (owner owner))
    "This setter protects against setting OWNER's `current' slot to an invalid object."
  