Meaning of browser headers?

This isn't really an HTML question, but as HTTP is the protocol most
often used to transport HTML, I thought some people here might have
some insights. Furthermore I'm not sure where else to ask.

Consider the following request headers (I used || to separate names and
values):

Accept||text/xml,application/xml,application/xhtml+xml,text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5
Accept-Charset||ISO-8859-1,utf-8;q=0.7,*;q=0.7
Accept-Encoding||gzip,deflate
Accept-Language||en-us,en;q=0.5

I'm curious what the q=0.5 , q=0.7 and so forth indicate. Can someone
enlighten me? Point me to a reference?

-Josh

On 04/08/2006 18:16, joshbeall (AT) gmail (DOT) com wrote:

[snip]

Accept||text/xml,application/xml,application/xhtml+xml,text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5
Accept-Charset||ISO-8859-1,utf-8;q=0.7,*;q=0.7
Accept-Encoding||gzip,deflate
Accept-Language||en-us,en;q=0.5

I'm curious what the q=0.5 , q=0.7 and so forth indicate.

They are referred to as "quality values" though that's a misnomer. They
indicate a relative weight, allowing the browser to specify which
content type, language, etc. is preferred. This allows the server to
choose the best possible representation (assuming there's more than one)
during content negotiation.

The values range from zero (0) to one (1), with at most three decimal
places. A value of zero means that item - character encoding, language,
whatever it may be - is not acceptable; the server should never return
something matching it. If there is no explicitly associated quality
value, it is assumed to be 1.0.

Can someone enlighten me? Point me to a reference?

RFC 2616[1] (HTTP/1.1) is the definitive reference. Quality values are
described in section 3.9 Quality Values. HTTP headers are listed within
chapter 14 Header Field Definitions.

Mike


[1] RFC 2616 Hypertext Transfer Protocol -- HTTP/1.1
<http://www.ietf.org/rfc/rfc2616.txt>