[tz] Extra transition for Europe/London with 2023d

[Guy Harris]

On Jan 6, 2024, at 2:30 PM, Stephen Colebourne via tz <tz at iana.org> wrote:

> On Sat, 6 Jan 2024 at 21:52, Guy Harris via tz <tz at iana.org> wrote:
> 
>> However, I'd still like to see what the people who use the source files to get STDOFF and SAVE information - and, for that matter, rule information - to give examples of how this is useful.
> 
> The various Java APIs all expose both the standard offset and the
> actual offset, and say that daylight savings is when the two differ.

Not that the decision to do so would be easily reversible, if reversible at all, just as the decision by the Bell Labs Research folks to expose a "DST is in effect at the date and time in question" member of struct tm would not be easily reversible, if reversible at all, but what was the rationale for exposing them both?  Was there a situation where a Java library or application needed that information?

>> So what do the (presumed) Booleans "dstLegal" and "dstSummer" mean here?
> 
> They allow the JSON file to express the difference between negative
> DST and "are the clocks > standard offset" DST.

(As one reason why tm_isdst was a mistake pops up again....)

Was this done before, or after, the "Ireland does things differently" issue popped up?