[lawaaiig]

That understanding is in line with using libresolv and the established behavior of the resolv.conf file, which accompanies the libresolv library. While it’s true that different implementations (e.g., some resolver stubs) might use various methods like round-robin, timing, or querying all servers simultaneously, this doesn’t invalidate the behavior outlined in resolv.conf.

Again, there can be other valid reasons for maintaining an order. Could be about latency, privacy etc.

I admit to not having read the full thread, and I apologize for any needless rehashing of arguments. It was just the first result confirming systemd-resolved breaking setups by its handling of what many (in that thread) consider expected behavior.

What I think you're primarily suggesting is that there are no formal standards prescribing glibc's behavior in terms of DNS resolution order. That is certainly true, and I don't disagree calling it an implementation detail.