How should clients fail on encountering invalid list members?

[johannhof]

This is a discussion I had previously with @cfredric: How should clients behave when a part of the list is invalid (e.g. no primary domain on a set)? Should they fail "gracefully" by only dropping the invalid part of the list (e.g. the affected set) or, given that the server should deliver correct information in all cases (and otherwise be informed about a malformed list, reject the entire list altogether?

We should come to an agreement and document that in the spec.

[dmarti]

I would prefer to have the client reject the entire list. This would mean more people would be likely to detect and report the problem. A graceful failure could result in a partly broken state persisting longer, which would be more likely to overlap with other things being partly broken and increase the total troubleshooting effort for web developers.