anchor.diff:    (:accessor-name-transformer #'class*:name-identity)
     (:documentation "Internal node of the history tree."))
   
  +(export 'value)
   (defmethod value ((node node))
     (value (entry node)))
   
  
positive.code:            :documentation "The key is an owner identifier (an artitrary balue),
  the value is an `owner'.")
     (current-owner-identifier (error "Owner identifier required")
                    :reader current-owner-identifier
                    :type t
                    :export t
                    :documentation "Must be one of the `owners' keys.")
     (entries (make-entry-hash-table)
              :type hash-table
              :documentation "The key is an `entry', the value is the list of
  nodes that hold this data.")
     (key #'identity
                :type function
                :documentation "The result of this function is passed to `test'
  and `hash-function'.  It is useful to uniquely identify (i.e. avoid
  duplications) objects from one of their slots.")
     (test #'equalp
  
negative.code: over two entries are equal.
  Also see `hash-function'.")
     (hash-function #'sxhash
                    :type function
                    :documentation "Function that returns the hash of the result
  of `key' called over an `entry'.
  Also see `test'."))
    (:export-class-name-p t)
    (:export-accessor-names-p t)
  