`prefetch` initiator appears to be unused

[bakkot]

This part of the fetch spec says that requests have an associated initiator, for which one of the possible values is prefetch (added in #659, so cc @yoavweiss and @annevk as the most likely people to know abou this). A table shortly below it says that prefetch initiator is used for "HTML’s <link rel=prefetch>". But neither the HTML spec nor the resource hints spec (the only other place I could think where it would be defined) make any mention of this. The resource hints spec doesn't even mention initiators at all.

Is there somewhere else I should be looking?

[yoavweiss]

It's used in whatwg/html#4115, which never landed, but which we should get back to.

/cc @domfarolino

[annevk]

https://w3c.github.io/webappsec-csp/ uses it as well.

[bakkot]

@annevk Sorry, by "uses" I meant that nothing creates such requests. CSP switches on request having an initiator of prefetch, but since nothing creates such request that part of the specification is effectively dead. (That's actually how this came up; I was trying to figure out what that part of the CSP spec did.)

[annevk]

Ah okay, so in part the history here is that browsers shipped a bunch of things without standardizing them properly and we've been slowly trying to fix that. (Another large hole here is that CSS doesn't really call into fetch.)

[annevk]

cc @noamr

[noamr]

whatwg/html#8111 fixes this.