Accessing the history of a `ref` in Clojure

Question

The documentation for ref shows a :max-history option and states that "refs accumulate history dynamically as needed to deal with read demands." I can see that there is history at the REPL, but I don't see how to find previous values of a ref:

user=> (def the-world (ref "hello" :min-history 10))
#'user/the-world
user=> (do
          (dosync (ref-set the-world "better"))
          @the-world)
"better"
user=> (let [exclamator (fn [x] (str x "!"))]
          (dosync
           (alter the-world exclamator)
           (alter the-world exclamator)
           (alter the-world exclamator))
          @the-world)
"better!!!"
user=> (ref-history-count the-world)
2

Presumably the-world has had the values "hello", "better", and "better!!!". How do I access that history?

If it is not possible to access that history, is there a datatype that keeps a history of its values that can be queried afterwards? Or is that why the datomic database was created?