anchor.diff:     (buffer :initarg :buffer :accessor buffer :initform nil)
      (prompter:constructor
       (lambda (source)
  -      (with-data-unsafe (history (history-path (buffer source)))
  +      (with-history (history (buffer source))
           (htree:all-forward-children history)))))
     (:export-class-name-p t))
   (define-user-class history-forwards-source)
  
positive.code:   "Open a new buffer displaying the whole history tree of a buffer."
    (with-current-html-buffer (output-buffer (format nil "*History-~a*" (id buffer))
                                             'nyxt/history-tree-mode:history-tree-mode)
      (with-data-unsafe (history (history-path buffer))
        (let ((mode (find-submode output-buffer 'nyxt/history-tree-mode:history-tree-mode))
              (tree (spinneret:with-html-string
                      (:ul (:raw (htree:map-owned-tree
  
negative.code:   (add-url-to-history url (buffer mode) mode)
    (reset-page-zoom :buffer (buffer mode)
                     :ratio (current-zoom-ratio (buffer mode)))
    (with-history (history (buffer mode))
      (sera:and-let* ((owner (htree:owner history (id (buffer mode))))
                      (node (htree:current owner))
                      (data (htree:data node))
  