[CSSWG][css-cascade-5] Updated WD of CSS Cascading and Inheritance Level 5

The CSS WG has published an updated Working Draft of the CSS Cascading and Inheritance Module Level 5:

https://www.w3.org/TR/css-cascade-5/

This CSS module describes how to collate style rules and assign values by way
of cascading and inheritance.

Level 5 adds “layers” to the cascade, along with a syntax for defining and
sorting those layers. In the same way that cascade origins provide a balance
of power between user and author styles, cascade layers provide a structured
way to organize and balance concerns within a single origin – such as element
defaults, third-party libraries, themes, components, and overrides.

The changes have been made since the previous Working Draft:
* Unlayered styles now have the lowest priority in normal origins, rather than the highest.

There remain a couple issues open on bikeshedding the exact syntax:
https://github.com/w3c/csswg-drafts/issues/5791 (nested layer name syntax)
https://github.com/w3c/csswg-drafts/issues/5840 (call them "layers" or...?)

Please review the draft, and send any comments to this mailing list, <www-style@w3.org>, prefixed with [css-cascade-5] (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,
-Miriam