Google announced they are now supporting the rel=”canonical” attribute within HTTP headers.
This enables webmasters to set up a canonical for linking to or from PDF files or other non-HTML based files.
One of the examples given by Google is that a “webmaster can signal to Google that the canonical URL for the PDF download is the HTML document by using a rel=”canonical” HTTP header when the PDF file is requested.”
This also comes in handy when you use a CDN (content delivery network) and the content is being served from many different URLs. You can now use the rel=”canonical” within the HTTP header to set up those redirects for that type of content.
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