anchor.diff:    ((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
  +   (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',
  
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:     ;; Solution: node's `data' should be a class with 2 slots: `payload' and `nodes'.
      ;; Then the `data' can be held in the stash only.
      ;;
      ;; Stash should use (make-hash-table :test 'equalp)
      ;;
      ;; We need to add a function to cleanup the stash.
      ;; - If it has only disowned nodes _not in the tree_, easy.
      ;; - If it has disowned nodes in the tree, we need to unbind all these nodes.
  