Notes from an offline discussion with @robertbastian

There is a general problem with ICU4X and ECMA compatibility regarding zoned formatting.

• ICU4X interprets a datetime as in the target timezone, so would format 11:00 in Los Angeles as 11:00, PST regardless of the local time.
• ECMA interprets a datetime as in the local timezone, so would format 11:00 in Los Angeles as 02:00, PST, if the user is in Berlin.

We would prefer having ICU4X's behavior, but ECMA does not expose the calculation, it's only implicitly done during formatting.

Possible solutions:

1. Have the user input the offset for the timezone manually, and add it to the date time in ICU4X. Pro: This will result in the same behavior as ECMA, formatting 11:00 as 02:00. Con: This will fail for edge cases such as DST changes.
2. Same thing, but subtract in ECMA, to get the ICU4X behavior.
3. Same thing, but only allow UTC datetimes - this resolves the edge cases.
4. Read a timezone database using FFI, and use it to adapt the ICU4X code to match ECMA. Pro: Everything will work great, no additional code size. Con: Can't be read on windows, the behavior will be the ECMA one, which is not desirable. Is additional work.

Options for next steps:

1. Remove all timezone formatting for now, and implement solution 4 later on.
2. Keep the user input of offsets, and the manual subtraction, so solution 3.