Document loop handlers in the guide

guide/loop_handlers.md

@@ -16,15 +16,23 @@ While the same can be accomplished using plain HTTP handlers,
 it is recommended to use loop handlers because they are well-tested
 and allow using built-in features like hibernation and timeouts.
 
-Callbacks
----------
-
-@todo Describe the callbacks.
-
 Usage
 -----
 
-@todo Explain how to use them.
+Loop handlers are used for requests where a response might not
+be immediately available, but where you would like to keep the
+connection open for a while in case the response arrives. The
+most known example of such practice is known as long-polling.
+
+Loop handlers can also be used for requests where a response is
+partially available and you need to stream the response body
+while the connection is open. The most known example of such
+practice is known as server-sent events.
+
+Loop handlers essentially wait for one or more Erlang messages
+and feed these messages to the `info/3` callback. It also features
+the `init/3` and `terminate/2` callbacks which work the same as
+for plain HTTP handlers.
 
 The following handler waits for a message `{reply, Body}` before
 sending a response. If this message doesn't arrive within 60

guide/toc.md

@@ -21,7 +21,6 @@ Cowboy User Guide
    *  Usage
  *  [Loop handlers](loop_handlers.md)
    *  Purpose
-   *  Callbacks
    *  Usage
  *  [Websocket handlers](ws_handlers.md)
    *  Purpose