Hi, Thomas.

The following NB comments have to do with difficulties we're facing in referring to Unicode features in the C++ standard. See also a rejected attempt to resolve these matters editorially here.

The issue that we are facing is that

  1. ISO/IEC 10646 specifies only a portion of the features specified in the Unicode Standard, and
  2. The C++ standard has normative dependencies on features from the Unicode Standard that are not specified by ISO/IEC 10646, and
  3. Use of an ISO/IEC 10646 standard that is not aligned with a use of a Unicode Standard results in problems like that reported in FR-021-013.

The ISO requires normative references to refer to an ISO standard when one is available as stated in section 10.2, Permitted referenced documents, in part 2 of the ISO/IEC Directives. That has so far been applied such that, when a Unicode feature is available in ISO/IEC 10646, we refer to that standard for that functionality; when not, we refer to the Unicode Standard. This has resulted in the situation that, as FR-010-133 states, we arguably reference, directly or indirectly, up to four distinct versions of the Unicode Standard.

Referring to both ISO/IEC 10646 and the Unicode Standard creates a burden with regard to how to align those references in order to reference a consistent set of Unicode features. The Unicode Standard is released once per year. ISO/IEC 10646 is released every three years, but amendments are issued to align the current release with new Unicode Standards as they occur. Some clever wording, thanks to section 10.4, Undated references, of the ISO/IEC Directives, would permit an undated reference to ISO/IEC 10646 to apply to the most recent amendment of that standard and enable a similarly undated reference to the Unicode Standard such that the references are aligned. That would solve the problem to a certain degree, but 1) requires us to provide wording that makes the relationship between the standards sufficiently clear, 2) retains a burden on implementors of having to consult both standards, and 3) puts us in the middle of any discrepancies found between the two standards.

SG16 discussed these issues during its 2022-11-02 telecon. A summary pertaining to these two NB comments is present in a GitHub issue comment for FR-010-133. SG16 took two polls, one of which demonstrated consensus for exploring whether we could discontinue referring to ISO/IEC 10646 in favor of referring only to the Unicode Standard. For ease of reference, here is the poll:

The consensus was not unanimous; there is some demand for more rigorous specification as demonstrated in ISO/IEC 10646 relative to the Unicode Standard.

That brings us to you, Thomas. As project editor, what options do you see? Is an argument that ISO/IEC 10646 is not (currently) suitable for our purposes due to its limited scope sufficient to replace references to it with references to the Unicode Standard? Is this a question that we would have to take up with the ISO directly and, if so, can we do so?

I'll be happy to answer any further questions you might have.

Tom.