[Cbor] draft-bormann-cbor-time-tag: POSIX and UTC are not the same

[Emile Cormier <[e-mail]>]

In draft-bormann-cbor-time-tag (tags 1001-1003), UTC and POSIX are
confounded together under the same value of 0, under section 3.4. Key -1:
Time Scale.

UTC and POSIX are not the same! Per https://en.wikipedia.org/wiki/Unix_time:

... leap seconds are ignored, with a leap second having the same Unix time
> as the second before it, and every day is treated as if it contains exactly
> 86400 seconds. Due to this treatment Unix time is not a true representation
> of UTC.
>

This is reinforced by the fact that C++ has distinct clocks for system time
and UTC:

https://en.cppreference.com/w/cpp/chrono/system_clock
https://en.cppreference.com/w/cpp/chrono/utc_clock

There should therefore be distinct values for POSIX and UTC.

Cheers,
Emile Cormier