[tz] More on EU/UK/Brexit clock changes

[Paul Eggert]

On 2/14/20 3:01 PM, Michael H Deckers wrote:
> a TZ string may well specify that the "alternative" time
>     is "permanent" (in the sense of being in force throughout the
>     year), for instance with:
>                         EET-2/BST-1,J1/01:00,J365/24:00

Good point; I hadn't thought about the possibility of using negative DST to 
specify permanent daylight saving time. Unfortunately, this TZ setting does not 
work in recent GNU/Linux systems, like Fedora 31:

$ TZ=EET-2BST-1,J1/01:00,J365/24:00 date -d at 1577833199
Tue Dec 31 23:59:59 BST 2019
$ TZ=EET-2BST-1,J1/01:00,J365/24:00 date -d at 1577833200
Wed Jan  1 01:00:00 EET 2020

Also, we know that many Java systems do not support negative DST. So even though 
the specific phrase quoted in the House of Lords document is incorrect, it's 
still the case that many practical systems don't support permanent DST.