anchor.diff:                  (if default-p
                       default
                       $empty-default))
  -               (pclass (if (member type (list 'cl:keyword 'cl:symbol))
  -                           'symbol
  -                           type))
                  (cslot (unless alias-for
                           (make-field-data
                            :internal-slot-name internal-slot-name
  
positive.code:                        :name  (or name (slot-name->proto slot))
                         :type type
                         :kind kind
                         :class pclass
                         :qualified-name (make-qualified-name *current-message-descriptor*
                                                              (or name (slot-name->proto slot)))
                         :label label
  
negative.code:                                ((and (not default-p)
                                       (eq label :optional)
                                       ;; Use unbound for booleans only
                                       (not (eq type 'boolean)))
                                  nil)
                                 (default-p `,default)))))
                 (field (make-instance
  