[CSSWG][css-contain-3] Updated WD of Containment L3

The CSS WG has published an updated Working Draft of Containment Level 3:

https://www.w3.org/TR/css-contain-3/

Containment indicates that an element’s subtree is independent of the rest of the page. This enables heavy optimizations by user agents. Level 3 defines inline-size containment, along with the terms, properties, units, and at-rule needed for Container Queries.

This update represents 8 months of refining the functionality and syntax based on feedback from both authors and implementors. For example:

• Queries are automatically resolved against a container that has the appropriate container-type, without additional syntax.
• Size queries are streamlined, and more similar to Media Queries, by removing the function-based syntax.
• Block-size container-type was removed, as it was not viable for implementors, and has few use-cases.
• In order for style-queries to work with inherited styles, all elements are style containers by default. That also removes the need for a container-type of style.
• General-enclosed is allowed in the query syntax, for the sake of forward compatibility.

Significant changes are all listed at:
https://www.w3.org/TR/css-contain-3/#changes-2021-12

Please review the draft, and send any comments to the www-style mailing list,
<www-style@w3.org>, prefixed with [css-contain-3] (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