Re: Document ordering guarantees on INSERT/UPDATE RETURNING clause

FWIW I've received feedback from a SQL Server engineer that one definitely should *not* depend on such ordering there, and that future optimizations (e.g. parallel insertion of many rows) could result in row ordering which differs from the lexical ordering of the VALUES clause.

That seems very reasonable; if the situation is similar on PostgreSQL, then I'd suggest making that very clear in the INSERT[2] and UPDATE[3] docs.