https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/X-DNS-Prefetch-Control notes that the default setting for this attribute is “ON” (“on” is enabled for http pages and disabled for https pages, for security reasons), so this tag is redundant and should be removed from your code.
https://www.w3.org/TR/resource-hints/ and https://www.w3.org/TR/2011/WD-html5-author-20110809/the-meta-element.html#attr-meta-http-equiv may be helpful should you want to include specific dns prefetching (but it’s not recommended). https://www.chromium.org/developers/design-documents/dns-prefetching explains the prefetch control a little deeper into the on/off in http vs. https context. The best policy is to leave it alone and let the browser handle this in the recommended default manner. Allowing users to manage their own security through their browser settings is the best policy: don’t mess with the prefetch control. Leave the control alone. Removing this redundant line from your code will resolve your error.
Regards,
Phaewryn J.D. O’Guin
[Phaewryn J_D_ O'Guin]
From: Trucsweb.com <webmestre@trucsweb.com>
Sent: Friday, January 18, 2019 1:10 PM - 13:10 PM
To: www-validator@w3.org
Subject: x-dns-prefetch-control
This message is from an external sender. Please be careful when clicking on links and attachments.
Hi,
Bad value x-dns-prefetch-control for attribute http-equiv on element meta<https://html.spec.whatwg.org/multipage/#the-meta-element>.
<meta http-equiv="x-dns-prefetch-control" content="on">
Thank'.s
