anchor.diff:  Is a security related chain handler that appropriately sets the
   `Content-Security-Policy` headers.
   
  -Content Security Policy (CSP) is an added layer of security that helps to detect and
  -mitigate certain types of attacks, including Cross Site Scripting (XSS) and data
  -injection attacks. These attacks are used for everything from data theft to site
  -defacement or distribution of malware.
  +Content Security Policy (CSP) is an added layer of security that helps to detect
  +and mitigate certain types of attacks, including Cross Site Scripting (XSS) and
  +data injection attacks. These attacks are used for everything from data theft to
  +site defacement or distribution of malware.
   
   Here a simple example on how to use it:
   
  
positive.code: 
  The possible values for the `:policy` key are: `:deny` and `:sameorigin`.
  
  WARNING: The frame-ancestors directive from the CSP Level 2 specification officially
  replaces this non-standard header.
  
  
  ==== Strict Transport Security
  
  This is a security related chain handler that adds the `Strict-Transport-Security`
  header to the response.
  
  HTTP Strict Transport Security (often abbreviated as HSTS) is a security feature
  that lets a web site tell browsers that it should only be communicated with using
  HTTPS, instead of using HTTP.
  
  Usage example:
  
  
negative.code: === 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.
  
  [source, clojure]
  ----
  