Define behavior of link headers

[noamr]

MDN: https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Link
Header spec: RFC 8288

Currently some browsers support the Link header, but that behavior is not specified in the HTML spec.
A link header can be preload or prefetch. prefetch is not yet spec'ed.
specifying early hints depends on this.

[domenic]

We have https://html.spec.whatwg.org/#processing-link-headers which is not much, but tries to handwave some stuff (like, it implies that stylesheet from Link headers come before stylesheets from <link> elements, in terms of cascade order and document.styleSheets.

https://html.spec.whatwg.org/#interactions-of-styling-and-scripting also has a note.

At a basic level, I wonder how many of the link types that are external resource links are also supported in header form.

[noamr]

Ah the spec a

We have https://html.spec.whatwg.org/#processing-link-headers which is not much, but tries to handwave some stuff (like, it implies that stylesheet from Link headers come before stylesheets from <link> elements, in terms of cascade order and document.styleSheets.

https://html.spec.whatwg.org/#interactions-of-styling-and-scripting also has a note.

At a basic level, I wonder how many of the link types that are external resource links are also supported in header form.

The spec actually points to a different issue, I guess this one should fold into that one.

[noamr]

(Closed as duplicate of #4224)