CET is not a variable timezone and should be defined as a UTC offset

[olivr70]

In timezone.ts, CET is defined as mixed timezone, with daylight saving time, like PT (Pacific Time) or some others.

This is not the case. CET is the standard time in Europe, used during the winter. It should just be defined

   CET: 60,

This introduces confusion and unexpected results when using date/time with explicit mention of CET.

This can be verified for example here.

Daylight saving times are extremly complex, and should probably be handled only with IANA Timezones (see (like Europe/Paris). They are supported by the Intl library and by the dayjs module. To get a glimpse of this complexity, one can check How to Read the tz Database Source Files

[wanasit]

Note: This is related to #552 (and #532).