[tz] [PROPOSED] Use "PST/PDT" for Philippine time

[Paul Eggert]

On 06/22/2018 04:18 PM, Michael H Deckers via tz wrote:
> I propose to record only what we really have learned since 2018e:
>    the abbreviation PST for Manila time was legally acknowledged
>    in 2013, and it was used later on by some newspapers. 


Generally speaking, tzdb uses current abbreviations even for older 
timestamps. That is, tzdb is designed primarily for today's uses, such 
as a historian writing today about events long ago; it does not attempt 
to record the long-ago abbreviations, such as the abbreviation Filipinos 
back in (say) 1950 used to describe time back in 1950. In that sense, it 
is like modern historians who systematically use the Gregorian calendar 
even when writing about events that took place in Russia in 1914.

Partly this is to simplify maintenance. That is, it's not merely that 
tzdb is designed for today's uses; it's also that it's easier to keep 
track of today's abbreviations than to also keep track of historical 
abbreviations used in the past. This point is covered in 
<https://data.iana.org/time-zones/theory.html>, which gives the 
following guideline for abbreviations:

--

Use current abbreviations for older timestamps to avoid confusion. For 
example, in 1910 a common English abbreviation for time in central 
Europe was 'MEZ' (short for both "Middle European Zone" and for 
"Mitteleuropäische Zeit" in German). Nowadays 'CET' ("Central European 
Time") is more common in English, and the database uses 'CET' even for 
circa-1910 timestamps as this is less confusing for modern users and 
avoids the need for determining when 'CET' supplanted 'MEZ' in common 
usage.