[tz] Irish Standard Time vs Irish Summer Time

[Michael Deckers]

   On 2017-12-08 08:26, Zefram wrote:

> That's not a change to the format that zic accepts.

   Well, I did not mean the input accepted by
   any particular implementation of zic but
   the public interface described in zic(8),
   the definition of the format of tzdb data.
   If some zic implementation accepts complex
   numbers as SAVE values that does not mean
   we can use it in tzdb data.

> zic already does allow negative AT times.

   Interesting. Allowing negative AT values would
   provide a "convenient notation" to avoid the
   Chatham Rules, as in

   Rule  NZ  2008  max  -  Apr  Sun>=1  -10:00u 0  S

> zic.8 ought to be patched to make explicit that AT and SAVE have no
> small range limits.

   Yes, and it may also be necessary to state the meaning
   of such extensions; for instance, the suffixes u, g, z
   currently are allowed for SAVE values but they
   cannot really be used because it is not clear what
   they are supposed to mean in this context.

   Michael Deckers.