Clarify what is "eligible third-party traffic"

[kostajh]

It would be nice to provide more details about what the proposal considers to be "eligible third-party traffic". The README says:

We’ll explore leveraging methods similar to other browsers and existing lists that identify these third parties.

I assume this means using some list like https://github.com/lightswitch05/hosts?

Will client-side code that makes requests to non-advertiser domains and subdomains be impacted by the proxy? For example, if visiting en.wikipedia.org, it's possible for client-side code to call other domains (login.wikimedia.org, commons.wikimedia.org) or subdomains (e.g. another language Wikipedia like el.wikipedia.org): should we anticipate that all such calls would get routed through the IP Protection proxy, because Chrome would see these requests as third-party traffic?