anchor.diff:  === SSE (Server-Sent Events)
   
   WebSockets are cool because they allow bi-directional communication, but in some
  -circumstances we only need something unidirectional, for notifying the client about
  -some changes or any other events. For this purpose exists
  -link:https://developer.mozilla.org/en-US/docs/Server-sent_events[Server-Sent Events]
  -(SSE) and _catacumba_ also has support for it.
  -
  -The handler for SSE does not differs much from websockets (that we have seen in the
  -previous section). The main difference is that server-sent events are unidirectional
  -and they only can send data in the server to client direction.
  +circumstances we only need something unidirectional, for notifying the client
  +about some changes or any other events. For this purpose exists
  +link:https://developer.mozilla.org/en-US/docs/Server-sent_events[Server-Sent
  +Events] (SSE) and _catacumba_ also has support for it.
  +
  +The handler for SSE does not differs much from websockets (that we have seen in
  +the previous section). The main difference is that server-sent events are
  +unidirectional and they only can send data in the server to client direction.
   
   [source, clojure]
   ----
  
positive.code: ----
  
  All handlers in the route pipeline that are going after the session handler will
  come with `:session` key in the context with a "atom" like object. You just treat it
  as atom, so for attaching some data to the session you should use the well known
  `swap!` function:
  
  [source, clojure]
  ----
  
negative.code:   the current server time to the client."
    [context]
    (ct/sse context
            (fn [{:keys [out ctrl]}]
              (go-loop []
                (when-let [_ (>! out (str (java.time.Instant/now)))]
                  (<! (timeout 1000))
  