Tim BrayAug 23, 2025

Three small announcements:
1. RFC 9839, a guide to which Unicode characters you should never use: https://www.rfc-editor.org/rfc/rfc9839.html
2. Blog piece with background and context, “RFC 9839 and Bad Unicode”: https://www.tbray.org/ongoing/When/202x/2025/08/14/RFC9839
3. A little Go library that implements 9839’s exclusion subsets: https://github.com/timbray/RFC9839

#Unicode

RFC 9839: Unicode Character Repertoire Subsets

This document discusses subsets of the Unicode character repertoire for use in protocols and data formats and specifies three subsets recommended for use in IETF specifications.

Show threadSimon JosefssonAug 24, 2025
@timbray Great work! You say the library is well tested, are there test vectors available somewhere? I would like to see support for identifying Bad Unicode as you specify added to https://www.gnu.org/software/libunistring/ and if I were to start working on that, I would like to see good test cases.
libunistring - GNU Project - Free Software Foundation (FSF)

Show threadTim Bray
@jas check out the unit tests in the repo, unichars_test.go - probably not in the right format for you, but the coverage is pretty exhaustive.
Aug 24, 2025 at 10:19amWeb