I wrote: >I've got plans for DT:TZ:Local. Another strand of this that might be of interest. I got thinking about the various mechanisms we have that try to DWIM with a ruleless SystemV-style zone spec (such as "GMT0BST"). The Olson database has the main US ones as links to appropriate geographical zones, and also (commented out) another version of them that just implements the US 1976 rules like DT:TZ:SystemV does. AIX and HP-UX both have systems in which the known geographical timezones are named in the SystemV style. DT:TZ has a couple of irregular aliases to Olson zones. In all of these cases, only a handful of zones are supported, and all by manual effort. I'd like to have a systematic approach to this.
Given the availability of the entire Olson database, we can look at every zone and pick out its abbreviations and offsets for any particular year we're interested in (or for all years within a broad range). In some cases there will be offset changes that don't fit into the SystemV scheme, but usually you'll be able to generate a ruleless SystemV-style spec that (partially) describes the behaviour of a zone in a particular year. Then, given such a ruleless zone spec, you can emit a list of all the candidate geographical zones. The most conservative potential use of this would be in a timezone selection widget: "you're currently configured for EST5EDT, do you want America/New_York, America/Chicago, ...?". A more advanced usage would be to automatically pick one of the candidates (on what basis I don't know) and either use the zone as a whole or apply its DST rules while staying within the POSIX limits of what the zone spec could mean. This could potentially be useful default behaviour somewhere within DT:TZ. -zefram
