It's only stable for case folding:

https://www.unicode.org/policies/stability_policy.html

"Caseless matching of Unicode strings used for identifiers is stable.

"For each string S containing only assigned characters in a given Unicode
version, toCasefold(toNFKC(S)) under that version is identical to
toCasefold(toNFKC(S)) under any later version of Unicode."
On Thu, Jul 10, 2025, 7:18 p.m. Thiago Macieira via Std-Proposals <
std-proposals_at_[hidden]> wrote:

> On Thursday, 10 July 2025 14:54:55 Pacific Daylight Time JJ Marr via Std-
> Proposals wrote:
> > A valid invocation of a normalization function should never change
> result.
>
> Can you quote the portion of the Unicode standard where they promise that?
>
> --
> Thiago Macieira - thiago (AT) macieira.info - thiago (AT) kde.org
> Principal Engineer - Intel Platform & System Engineering
>
>
>
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