# RFC 2616 HTTP/1.1

- Content Negotiation (chapter 12)

  > The mechanism for selecting the appropriate representation when servicing a request.

- Server driven
  - Client sends
    - Accept (14.1): `image/png`
    - Accept-Charset (14.2): `utf-8`
    - Accept-Encoding (14.3): `gzip`
    - Accept-Language (14.4): `da, en-gb;q=0.8, en;q=0.7`
    - User-Agent (14.43)
  - Server sends: Vary (14.44)