Proposed resolution (approved by CWG 2022-10-21):

Change in E.4 [uaxid.pattern] as follows:

UAX #31 describes how formal languages that use or interpret patterns of characters, such as regular expressions or number formats, may describe that syntax with Unicode properties such as computer languages should describe and implement their use of whitespace and syntactically significant characters during the processes of lexing and parsing.

C++ does not do this as part of the language, deferring to library components for such usage of patterns. This requirement does not apply to C++ claim conformance with this requirement.

[Accepted as a DR at the November, 2022 meeting.]

Unicode 15.0 UAX #31 clarified that rule R3 was, in fact, intended to apply to programming languages. WG21's prior understanding was that programming languages are not in scope of that rule. The proposed resolution updates E.4 [uaxid.pattern] to the revised understanding. See paper P2653R1 (Update Annex E based on Unicode 15.0 UAX 31) for more details.