I was wondering if you should pick the `right[key]` value as it leads to a predictable outcome, i.e. the last conflicting value is always the one.  Otherwise in a list of N tables (e.g. for `hstack`) which all conflict, I think this leads you to get the N-1 value, which is sort of confusing to explain.  I thought of this when see the doc string that says to `pick one of the meta-data values`, but doesn't say which.  Does this make sense?