[CSSWG][css-values-4] FPWD of CSS Values and Units Level 4

The CSS WG has published a First Public Working Draft of the
CSS Values and Units Module Level 4:

     https://www.w3.org/TR/css-values-4/

This CSS module describes the common values and units that CSS
properties accept and the syntax used for describing them in
CSS property definitions.

Additions since Level 3 consist of:

   * the vi, vb, ic, cap, lh and rlh units.
   * min(), max(), and clamp() functional notations
   * unit arithmetic to calc(), e.g. calc(1vh / 1rem * 0.2ch)
   * toggle() (punted from level 3)
   * defined serialization of math functions

Please review the draft, and send any comments to this mailing list,
<www-style@w3.org>, prefixed with [css-values] (as I did on this
message) or (preferably) file them in the GitHub repository at
   https://github.com/w3c/csswg-drafts/issues

For the CSS WG,
~fantasai