Re: [w3ctag/design-reviews] `Accept-CH` header is weird (#206)

Discussed at London F2F.  TAG's group conclusion is that this header needs to be reconsidered.  Our primary concern is the redirection that it incentivises.  We believe many sites will choose to bounce non-bot users through a redirect in order to farm the CH data before rendering a first page. As the number of CH headers increases, this motivation will only get stronger. There is a strong precedent for web authors doing things that implementors think are bad ideas (eg. naive user agent header parsing).

This will leave Client-Hints in a position marginally better than serving a script to sample the data in JS and then setting it in a cookie and doing a redirect, but not by much.  It doesn't achieve the goal of client hints.

It's worth noting that there are numerous examples of major sites doing redirects on a first request.  And also that many site authors will go to considerable lengths to avoid an inconsistent experience between the first and second page views.  Additionally, if subresource requests within a page get different CH headers to the page itself, the subresources run the risk of not being compatible with the page into which they are being loaded.

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