

Google now supports link rel="canonical" in HTTP headers - nephics
http://googlewebmastercentral.blogspot.com/2011/06/supporting-relcanonical-http-headers.html

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wnoise
The first comment has it spot-on for the first example: the html version is an
alternate version -- it's not the same content. The example of content
distribution networks (and other mirrors) is much better.

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techvibe
The syntax is very strange.

rel-canonical: <http://www.example.com/white-paper.html>

would have been a better one.

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tav
The Link: header has been a part of the HTTP spec since forever. The following
example from the HTTP/1.1 spec [1] should look familiar:

    
    
        Link: <http://www.cern.ch/TheBook/chapter2>; rel="Previous"
    

We should be applauding Google for supporting standard headers instead of
making up new ones. The Link: header is even mentioned in the HTTP 1.0 spec
[2] and, as mentioned in the OP, there's even an RFC acting as a registry for
the various Link relation types [3].

Though I don't always agree with standards, I hope you'd agree that it really
does make sense in this case...

[1] <http://tools.ietf.org/html/rfc2068#section-19.6.2.4>

[2] <http://tools.ietf.org/html/rfc1945#appendix-D.2.6>

[3] <http://tools.ietf.org/html/rfc5988#section-5>

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lamnk
What's the difference with the <link rel="canonical"> tag ? For those
documents that are not HTML ? Seem not very useful to me.

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pierrefar
It works for both HTML documents and non-HTML files. For non-HTML files, you
cannot use the HTML link rel="canonical" tag, so this new support for the
header is the only option.

