Henri SivonenToday in Web compat: Firefox and Safari are ahead of Chrome in ICU4C version and upsteam ICU4C changed the formatting of zero offset from GMT. This broke birthday date validation for a UK based site for birthdays before 1970 in Firefox and, on 26.x Apple OSs, in Safari, because the site performs a formatting-based check on the time zone of London on the date to be validated and the UK has changed time zone rules along the way.
It turned out that some time zones that use “GMT” as their abbreviation in the same style as CET for Central European Time or PDT for Pacific Daylight-saving Time previously got “GMT” by a different mechanism, so an intentional change to that mechanism had unintended effects.
The time zone and daylight-saving time fans out there will probably appreciate the user impact description that I wrote for release management:
“Users whose birthday is before the end of October 1971 on a day when the UK was not observing daylight-saving time can't sign up for online banking at a particular British bank.”
mkj
Dominik Röttsches@hsivonen https://chromium-review.googlesource.com/c/chromium/src/+/7623512 ICU roll landed and is coming in Chrome 148. We kept GMT instead of GMT+0 in http headers due to that being hard coded in the respective RFC, but for JS date formatting we should conform to new Unicode rules.
@drott It turned out that while the CLDR change was intentional, this particular outcome was not. https://unicode-org.atlassian.net/browse/CLDR-19362