[css-shadow-parts-1] First Public Working Draft of the CSS Shadow Parts Level 1

The CSS WG has published a First Public Working Draft of the CSS Shadow
Parts Level 1.

    https://www.w3.org/TR/css-shadow-parts-1/

This new specification allows an author to specify that certain “parts” of
a shadow tree are exposed on the shadow host for styling by the outer page
(rather than being hidden away and only styleable by the component itself).
The new ::part() selector allows the outer page to refer to those exposed
parts.

This allows a web component author to get the encapsulation benefits of
using Shadow DOM for the internals of their component, while still allowing
parts of it to be styled with the full flexibility of normal CSS.

See
https://developer.mozilla.org/en-US/docs/Web/Web_Components/Using_shadow_DOM
for a refresher on what Shadow DOM is, or the DOM spec (
https://dom.spec.whatwg.org/) for technical details.

Please review the draft, and send any comments to this mailing list,
<www-style@w3.org>, prefixed with [css-shadow-parts-1] (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,

Fergal Daly,
Tab Atkins.