On Mar 7, 2026, at 4:17 PM, Paul Eggert via tz <[email protected]> wrote: > On my Ubuntu 25.10 platform, my email client (Thunderbird) uses the GNU C > library to read TZif data. I was talking about that usage, not any ICU usage.
...or any usage by anything else not using the C API. So that's a case of an independent reimplementation of the same C/POSIX API that the tzcode implements. And it's not "my email client", it's "any code on my machine that uses that C/POSIX API", probably including, for example, "ls". That (re)implementation is intended to be compatible with other implementations; it probably exists because of a combination of licensing reasons and perhaps "not wanting ties to tzcode release schedules" reasons, and it's somewhat subject to the same constraints as the tzcode implementation, although the GNU folks are known to discard some POSIX constraints without a thought other than "don't like it, set POSIXLY_CORRECT in the environment" (e.g., getopt() behaves, by default, in some user-visibly non-POSIX-compliant ways).
