Change:
A client MAY additionally use a discovered Designated Resolver without either of these methods, based on implementation-specific policy or user input.  Details of such policy are out of scope of <del> this document.  Clients SHOULD NOT automatically use a Designated </del> <ins> this document.  Clients MUST NOT automatically use a Designated </ins> Resolver without some sort of validation, such as the two methods defined in this document or a future mechanism. <del> A client MUST NOT use a Designated Resolver designated by one Unencrypted Resolver in place of another Unencrypted Resolver.  As these are known only by IP address, this means each unique IP address used for unencrypted DNS requires its own designation discovery. This ensures queries are being sent to a party designated by the </del> <ins> A client MUST NOT re-use a designation discovered using the IP address of one Unencrypted Resolver in place of any other Unencrypted Resolver.  Instead, the client SHOULD repeat the discovery process to discover the Designated Resolver of the other Unencrypted Resolver. In other words, designations are per-resolver and MUST NOT be used to configure the client's universal DNS behavior.  This ensures in all cases that queries are being sent to a party designated by the </ins> resolver originally being used. 4.1.1. <del> Generally, clients also SHOULD NOT reuse the Designated Resolver discovered from an Unencrypted Resolver over one network connection in place of the same Unencrypted Resolver on another network connection.  Instead, clients SHOULD repeat the discovery process on the other network connection. </del> <ins> If a client is configured with the same Unencrypted Resolver IP address on multiple different networks, a Designated Resolver that has been discovered on one network SHOULD NOT be reused on any of the other networks without repeating the discovery process for each network. </ins> However, if a given Unencrypted Resolver designates a Designated Resolver that does not use a private or local IP address and can be

Discussion:
Addressing the comments in
Why the following isn't a MUST NOT? Clients SHOULD NOT automatically use a Designated Resolver without some sort of validation, such as the two methods defined in this document or a future mechanism. This bit is puzzling: A client MUST NOT use a Designated Resolver designated by one Unencrypted Resolver in place of another Unencrypted Resolver. There seems to be some context missing to explain why a client should found itself in that position. What I seem to understand from the text that follows: As these are known only by IP address, this means each unique IP address used for unencrypted DNS requires its own designation discovery. This ensures queries are being sent to a party designated by the resolver originally being used. is that clients must go through the designation process when their network attachment changes / they are re-configured WRT their UR. And that's because there is strict administrative coupling between a UR and its DRs that would be subverted otherwise. I am scanning this for the first time and I may be off on a tangent space, but if my reading is correct, then the text could be reorganised a bit to make the context for the requirement clearer. I found this other bit hard to parse: Generally, clients also SHOULD NOT reuse the Designated Resolver discovered from an Unencrypted Resolver over one network connection in place of the same Unencrypted Resolver on another network connection. What about: If a client is configured with the same Unencrypted Resolver's IP address on two different networks n1 and n2, a Designated Resolver that has been discovered on n1 SHOULD NOT be reused on n2 without repeating the discovery process. instead? In the IANA section IANA is requested to add an entry in "Transport-Independent Locally-Served DNS Zones" registry for 'URL' with the description "DNS Resolver Special-Use Domain", listing this document as the reference. Ignorant question: is there an associated delegation of 'URL' needed in the '.arpa.' zone? Or is that not necessary?
NAME could you take a pass at this? (For the .arpa one, we shouldn't do anything to the arpa zone)