To be clear, ATT is the system Apple put in place for native apps that is enforced by the App Store review process. When it comes to the browser, I think you’re more interested in Intelligent Tracking Prevention (ITP).
You should check out WebKit‘s tracking prevention policy:
You should check out WebKit‘s tracking prevention policy:
https://webkit.org/tracking-prevention-policy/
Also the Privacy category on the WebKit blog:
https://webkit.org/blog/category/privacy/
Specific blog posts you might be interested in are:
https://webkit.org/blog/7675/intelligent-tracking-prevention...
https://webkit.org/blog/9521/intelligent-tracking-prevention...
https://webkit.org/blog/10218/full-third-party-cookie-blocki...
https://webkit.org/blog/11338/cname-cloaking-and-bounce-trac...
https://webkit.org/blog/11545/updates-to-the-storage-access-...
https://webkit.org/blog/15697/private-browsing-2-0/