Lists in TeX's "mouth"
The package was developed to provide flexible lists, whose ordering can be altered on the fly. The implementation involves a pile of lambda-calculus and list-handling macros of an incredibly obtuse nature. The TUGboat paper serves as a manual for the macros. Having said all of which, confidence is enhanced by the knowledge that the TeX code was formally verified.
You can contact the maintainers of this package via email at
texlive dash maintainers at fedoraproject dot org.