Speculation rules: tag field

[domenic]

This proposal allow developers to specify a tag field in their speculation rules. This is used to compose a Sec-Speculation-Tags header, which is sent along with same-site prefetch and prerender requests.

The main use case is allowing the server to know which of several parties (e.g. individual page developer, framework, CMS, or CDN) is responsible for a given speculative load.

Request for Mozilla Position on an Emerging Web Specification

• Specification title: Speculation Rules
• Specification or proposal URL (if available): no spec yet, but it will be a part of https://wicg.github.io/nav-speculation/speculation-rules.html
• Explainer URL (if available): https://github.com/WICG/nav-speculation/blob/main/speculation-rules-tags.md
• Proposal author(s) (@-mention GitHub accounts): @domenic
• MDN URL (optional): will be added to https://developer.mozilla.org/en-US/docs/Web/HTML/Element/script/type/speculationrules
• Mozillians who can provide input (optional): @zcorpan and @bgrins participated recently in Speculation Rules - Navigational prefetching and prerendering #620
• WebKit standards-position: Navigational prefetching and prerendering WebKit/standards-positions#54 (comment)

Other information

I was unsure whether it's worth asking for a position on specific new additions to the speculation rules syntax, which was judged holistically in #620 as neutral.

I erred on the side of asking for more input, but, please let me know if there's a preferred path for future such additions.