[CSSWG][css-sizing-4] FPWD CSS Sizing L4

The CSS WG has published a First Public Working Draft of the CSS Box Sizing 
Module Level 4:

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

This module defines the sizing properties (width/height/etc.) and their 
keywords. It is currently drafted as a delta spec over css-sizing-3:
     https://www.w3.org/TR/css-sizing-3/

Additions since Level 3 include:
   * 'stretch' and 'fit-content' keywords for the sizing properties,
     which were deferred from L3.
   * the new 'aspect-ratio' property
   * the new 'contain-intrinsic-size' property

Note: The editors are still working on defining the relationship of 
'aspect-ratio' and the intrinsic sizing keywords, so don't expect too much 
clarity on that point.

Please review the draft, and send any comments to this mailing list,
<www-style@w3.org>, prefixed with [css-sizing-4] (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