;; I wonder if this slot option and the previous could be merged,
;; so that :base and :key remain keyword options, but :db-kind
;; :join becomes :db-kind (:join <db info .... >)?
;; I wonder if this slot option and the previous could be merged,
;; so that :base and :key remain keyword options, but :db-kind
;; :join becomes :db-kind (:join <db info .... >)?