] Much discussion about the representation of timestamps, the ] inability to predict future leap seconds, and the effects of ] out-of-date leap-second tables, I think if we all stipulate that some form of "display UTC" is the only representation that should be stored or forwarded, then some of the objections will disappear. If anyone wants to define such a "display UTC" representation for files or communication protocols, so be it. [Personally, I would just use an ISO string and eat the conversion and storage costs.] Otherwise, the local representation of timestamps is a local issue, and we should just be specifying an API to manipulate such timestamps in useful ways. [I'm not sure if making them arithmetic would be a advantageous step in that process.]