Goodbye FLoC, hello Topics

>Advertisers (and others) can request information via a JavaScript call to document.browsingTopics(), which will return zero to three Topic IDs, one for each of the previous three weeks, in a random order. The top five Topics for a given week are collected and one random Topic chosen from the full list is added in; one of those six Topics will be chosen for the week. In addition, Topics are tracked in a somewhat complicated scheme to try to "prevent the direct dissemination of user information to more parties than the technology that the API is replacing (third-party cookies)". Said scheme restricts sending Topics to callers that have already called the Topics API for the user on another site that shares a Topic ID with the site in question. So browsers can only send a Topic ID if the advertiser has asked for Topics from a related site (i.e. one that shares the Topic). The GitHub site has a lengthy example to show how it all works.

This sounds horrifyingly convoluted. I'm sure a smarter person than me can find lots of counter-intuitive ways to leak information from that mess by making repeated calls, for example from lots of throwaway sites with different topics.