The Accept-Encoding request-header field is similar to Accept, but restricts the content-coding values (section 14.12) which are acceptable in the response.
Accept-Encoding = "Accept-Encoding" ":"
#( content-coding )
An example of its use is
Accept-Encoding: compress, gzip
If no Accept-Encoding header is present in a request, the server MAY assume that the client will accept any content coding. If an Accept- Encoding header is present, and if the server cannot send a response which is acceptable according to the Accept-Encoding header, then the server SHOULD send an error response with the 406 (Not Acceptable) status code.
An empty Accept-Encoding value indicates none are acceptable.