To support content negotiation use cases such as differential serving of variable fonts, color vector fonts, responsive images, and other third-party content which requires client information lost by user agent reduction. For example: variable fonts allow significantly less font information to be transferred without loss of functionality, but only works on specific operating systems.
It’s already possible to set a Permissions Policy in the HTTP response header, but for sites without the ability to modify HTTP headers a HTML solution would be ideal. This proposal ships a meta tag which allows delegation of client hints to third-party origins. These tags could be included in code-snippets for embedded third-party content for ease of use.
For example, to specify third party requests to `https://foo.bar` must include `sec-ch-width` you could include:
<meta name="accept-ch" content="sec-ch-width=( https://foo.bar )">
You may still omit the permission policy and rely on the default allowlist as follows:
<meta name="accept-ch" content="sec-ch-width">
Note that this is the equivalent of the following today:
<meta http-equiv="accept-ch" content="sec-ch-width">
We do not anticipate compatibility risks for this addition - Blink currently implements first party client hints via a `http-equiv` meta tag, and that functionality will not be removed or modified.
Web developers: Positive interest from Cloudinary
Any improperly formatted client hint meta tags will be flagged in the Issues tab.
Is this feature fully tested by web-platform-tests?
Link to entry on the Chrome Platform Status