Representation header

A representation header is an HTTP header that describes one particular representation of a resource.

Representations are different forms of a particular resource.

For example, the same data might be formatted as a particular media type such as XML, JSON, HTML or Markdown, or localized to a particular written language or geographical region. The underlying resource is semantically the same in each case, but its representation is different.

While representations are different forms of resources, representations can themselves also be transmitted in various forms: an HTTP message frames (cf., e.g., HTTP/1.1's Transfer-Encoding), a particular stream of octets (cf., e.g., Content-Range) derived from the selected representation.

Clients specify the formats that they prefer to be sent during Content Negotiation (using Accept-* headers), and the representation headers tell the client the format of the selected representation they received.

Representation headers may be present in both HTTP request and response messages with various methods. If sent as a response to a HEAD request, they describe the body content representation that would be selected if the resource was requested with a GET request.

Representation headers include: Content-Type, Content-Encoding, Content-Language, Content-Range, Repr-Digest, and Digest Deprecated .