The CSS Working Group has published a First Public Working Draft of CSS Values and Units Module Level 5. This CSS module describes the common values and units that CSS properties accept and the syntax used for describing them in CSS property definitions.
https://www.w3.org/news/2024/first-public-working-draft-css-values-and-units-module-level-5/
what I did always miss, is _where_ we currently can use functions (maybe did overread it).
Recently I was astonished about a perfect hexagon with simple
aspect-ratio: 1/cos(30deg);
clip-path: polygon(50% -50%,100% 50%,50% 150%,0 50%);