[tz] Yukon to move to year-round PDT

[Paul Eggert]

On 3/9/20 1:24 PM, Brian Inglis wrote:
> Current official practice seems to be to use daylight saving time zone names in
> summer, and standard time zone names in winter.

Are you saying that people in Dawson Creek, Ft Nelson and Creston 
consistently say that they observe PDT in winter and MST in summer? My 
impression is that they don't much care what you call it, so long as you 
get the right clock setting. The press release announcing the 2015 for 
Fort Nelson 
<https://www.northernrockies.ca/assets/Home/Press~Releases/NRRM_Time_Change_Press_Release%202.pdf>, 
for example, says "The Northern Rockies Regional Municipality has 
resolved to remain on Mountain Standard Time (Pacific Daylight Time) 
throughout the entire year".

As I see it, the options compatible with current POSIX are the 
equivalent of:

* TZ='MST7' (MST all year, as standard time)

* TZ='PDT7' (PDT all year, as standard time)

* TZ='MST7PDT7,M3.2.0,M11.1.0' (MST in winter as standard time, PDT in 
summer as daylight saving time, and both are UTC -7)

None of these are entirely satisfactory. The first option is what we've 
been using in Dawson Creek etc., which is why it's in the draft tzdata 
now for Yukon.