About This HTML Issue
The Accept-CH value is not a valid value for the http-equiv attribute on a <meta> element according to the HTML specification.
The http-equiv attribute on <meta> only accepts a specific set of values defined in the HTML standard. These include content-type, default-style, refresh, x-ua-compatible, and content-security-policy. The Accept-CH header is used for Client Hints, which lets the server request specific information from the browser (like device width or viewport size), but it must be delivered as an actual HTTP response header from the server — not as an HTML <meta> tag.
While some browsers may process Accept-CH in a <meta> tag, this behavior is non-standard and not universally supported. The W3C validator correctly flags it as invalid. To fix this, move the Accept-CH directive to your server’s HTTP response headers.
Invalid Example
<head>
<meta http-equiv="Accept-CH" content="DPR, Viewport-Width, Width">
<title>My Page</title>
</head>How to Fix
Remove the <meta> tag and configure your server to send the header instead. For example, in an Apache .htaccess file:
Header set Accept-CH "DPR, Viewport-Width, Width"Or in Nginx:
add_header Accept-CH "DPR, Viewport-Width, Width";This ensures the Client Hints are delivered through a proper HTTP header, which is both valid and more reliably supported across browsers.
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