anchor.diff:      ;; disowned nodes.
       ;;
       ;; Alternative: Browse the nodes of the deleted owner, unbind each disowned
  -    ;; node, and for every owned node that has a disowned parent, rebind it to
  +    ;; node, and for every (child) owned node that has a disowned parent, rebind it to
       ;; the root.  We lose more information this way, but it's easier.
       owner))
   
  
positive.code: ;; TODO: Unexport most (all?) slot writers.
  ;; TODO: Review docstrings.
  ;; TODO: Is "Shared history tree" a better name than "Global history tree"?
  
  (defmacro export-always (symbols &optional (package nil package-supplied?)) ; From serapeum.
    "Like `export', but also evaluated at compile time."
  
negative.code:   ((origin nil ; TODO: Rename to `root'?  Not to be confused with the htree root, but maybe it's convenient to have the same method name.
             :type (or null node)
             :documentation "The first node created for this owner.")
     (creator nil                         ; TODO: Should it be an `owner' or an
                                          ; identifier?  An identifier would allow
                                          ; us to keep this information even afer
                                          ; the creator `owner' is deleted.
              :type t
              :documentation "The owner in `origin's parent node that created this owner.
  Unless the parent was disowned by this `creator',
  