Clarify behavior with subresource requests and subframe navigations

[letitz]

Subresource requests and subframe navigations are simpler as they cannot introduce a new first-party context. If the request matches the first-party URL's owner's manifest but is not currently recorded as being in that first-party set, the browser validates membership as above before making the request. Any Sec-First-Party-Set headers are ignored and, in particular, the browser should never read or write state for a first-party set other than the current one. This simpler process also avoids questions of retrying requests. The minVersion parameter in the header ensures that the browser's view of the owner's manifest is up-to-date enough for this logic.

I don't follow this paragraph.

1. I feel like a word is missing from the second sentence. What does it mean for a request to match a manifest? The "not currently recorded as being in that first-party set" makes me think the object is a registrable domain? Was the intention to say "the registrable domain of the fetched resource", or somesuch?

2. What does it mean for the browser to validate membership before making the request?

Maybe a couple of example request flows would help clarify the expected behavior here.