This page used to hold a proposal for a possible generic mechanism to allow authors to define custom text-transforms.

Wikis are good to sketch ideas, but not ideal to maintain specifications, so this has been moved to the author's personal site: https://specs.rivoal.net/css-custom-tt/

Feedback welcome on that page. You may also consult old version of this wiki page at https://wiki.csswg.org/ideas/at-text-transform?do=revisions