On 1/5/24 11:26 AM, Jonathan Wakely via SG16 wrote:
> Since the adoption of P2736 C++23 and the current C++ working draft
> just refer to "the Unicode Standard", with a URL referring to the
> latest version. We removed the bibliography entry for TR29 revision
> 35. P2736 gives the justification for this that the revision of #29
> included in Unicode 15 (revision 41) is just a bug fix, so there's no
> problem referring to that instead.
>
> That might have been true last year, but the current Unicode Standard
> (15.1.0) includes revision 43 of UAX #29, which makes significant
> changes to the extended grapheme cluster breaking rules. A new state
> machine is needed (and new lookup tables of properties) to implement
> rule GB9c. That's not just a bug fix, is it?
>
> Are C++ implementations expected to implement rule GB9c, despite it
> not being part of the standard when C++23 was published? If not, where
> in the C++23 standard does it say that implementations should conform
> to version 15.0.0 of the Unicode Standard, rather than version 15.1.0,
> or whatever version they publish next? How can we conform to a moving
> target?
>
> Am I missing some reference that names Unicode 15.0.0?

Thank you for raising this issue, Jonathan.

For reference, relevant SG16 discussions are recorded as follows:

  * 2022-11-02 SG16 meeting
    <https://github.com/sg16-unicode/sg16-meetings/blob/master/README-2022.md#november-2nd-2022>:
      o Includes discussion of FR-010-133
        <https://github.com/cplusplus/nbballot/issues/412> and
        FR-021-013 <https://github.com/cplusplus/nbballot/issues/423>.
        The following polls were taken:
      o *Poll 3: [FR-010-133][FR-021-013]: SG16 requests that the
        project editor discuss with the ISO the option of eschewing
        references to ISO/IEC 10646 in favor of the Unicode Standard
        both for technical consistency and release frequency.*
        Attendees: 9 (1 abstention)
        Objection to unanimous consent.
        SF
         F
         N
         A
         SA
        3
         3
         0
         1
         1

        Weak consensus
        SA: Use of the ISO/IEC 10646 document benefits from ISO governance.
        SA: Would prefer to explore expansion of ISO/IEC 10646 to
        include more components of Unicode.
      o *Poll 4: [FR-010-133][FR-021-013]: SG16 recommends resolving
        these comments by restricting all references to the Unicode
        Standard to the version that corresponds to the referenced
        version of ISO/IEC 10646.*
        Attendees: 9 (1 abstention)
        SF
         F
         N
         A
         SA
        2
         3
         0
         3
         0

        No consensus.
        A: It doesn't benefit the community to reference a Unicode
        version that is outdated by the time the standard is published.
  * 2022-11-30 SG16 meeting
    <https://github.com/sg16-unicode/sg16-meetings/blob/master/README-2022.md#november-30th-2022>:
      o Includes discussion of FR-010-133
        <https://github.com/cplusplus/nbballot/issues/412> and
        FR-021-013 <https://github.com/cplusplus/nbballot/issues/423>.
        No polls were taken.
  * 2022-12-14 SG16 meeting
    <https://github.com/sg16-unicode/sg16-meetings/blob/master/README-2022.md#december-14th-2022>:
      o Includes discussion of a draft of P2736R0. No polls were taken.
  * 2023-01-11 SG16 meeting
    <https://github.com/sg16-unicode/sg16-meetings#january-11th-2023>:
      o Includes discussion of P2736R0. No polls were taken.
  * 2023-01-25 SG16 meeting
    <https://github.com/sg16-unicode/sg16-meetings#january-25th-2023>:
      o Includes discussion of P2736R0. The following polls were taken:
      o *Poll 1.1: Whether __STDC_ISO_10646__ is predefined and if so,
        what its value is, are implementation-defined, retaining the
        mandated yyyymmL form.*
        Attendees: 11 (3 abstentions)
        SF
         F
         N
         A
         SA
        6
         2
         0
         0
         0

        Unanimous consent.
      o *Poll 1.2: Forward P2736R1, amended as discussed, to CWG and LWG
        as the recommended resolution of NB comments FR-010-133 and
        FR-021-013.*
        Attendees: 10 (1 abstention)
        SF
         F
         N
         A
         SA
        7
         2
         0
         0
         0

        Unanimous consent.

Tom.