clarify dox

src/metabase/driver/metadata.clj

@@ -2,7 +2,8 @@
   "Metadata multi-methods. Implemented by the various drivers, e.g. `metabase.driver.postgres.metadata`.")
 
 (defn- field-info-dispatch
-  "Dispatch fn for the various field info multi-methods. (Dispatches on kw like `:postgres`)"
+  "Dispatch fn for the various field info multi-methods. When calling a method like `field-count`, FIELD's Database
+   is fetched and we dispatch on it's `engine` (as a keyword). e.g. `:postgres`"
   [{:keys [db] :as field}]
   (let [{:keys [engine]} @db]
     (require (symbol (str "metabase.driver." engine ".metadata")))  ; dynamically load the correct driver implementation