http - Accept and Accept-Charset - Which is superior?

Question

In HTTP you can specify in a request that your client can accept specific content in responses using the accept header, with values such as application/xml. The content type specification allows you to include parameters in the content type, such as charset=utf-8, indicating that you can accept content with a specified character set.

There is also the accept-charset header, which specifies the character encodings which are accepted by the client.

If both headers are specified and the accept header contains content types with the charset parameter, which should be considered the superior header by the server?

e.g.:

Accept: application/xml; q=1,
        text/plain; charset=ISO-8859-1; q=0.8
Accept-Charset: UTF-8

I've sent a few example requests to various servers using Fiddler to test how they respond:

Examples

W3

Request

GET http://www.w3.org/ HTTP/1.1
Host: www.w3.org
Accept: text/html;charset=UTF-8
Accept-Charset: ISO-8859-1

Response

Content-Type: text/html; charset=utf-8

Google

Request

GET http://www.google.co.uk/ HTTP/1.1
Host: www.google.co.uk
Accept: text/html;charset=UTF-8
Accept-Charset: ISO-8859-1

Response

Content-Type: text/html; charset=ISO-8859-1

StackOverflow

Request

GET http://stackoverflow.com/ HTTP/1.1
Host: stackoverflow.com
Accept: text/html;charset=UTF-8
Accept-Charset: ISO-8859-1

Response

Content-Type: text/html; charset=utf-8

Microsoft

Request

GET http://www.microsoft.com/ HTTP/1.1
Host: www.microsoft.com
Accept: text/html;charset=UTF-8
Accept-Charset: ISO-8859-1

Response

Content-Type: text/html

There doesn't seem to be any consensus around what the expected behaviour is. I am trying to look surprised.

Answer 1

Altough you can set media type in Accept header, the charset parameter definition for that media type is not defined anywhere in RFC 2616 (but it is not forbidden, though).

Therefore if you are going to implement a HTTP 1.1 compliant server, you shall first look for Accept-charset header, and then search for your own parameters at Accept header.