[CSSWG][css-contain] PR of CSS Containment Module Level 1; FPWD of Level 2

The CSS WG has published a Proposed Recommendation of the CSS Containment Module Level 1:


This CSS module describes the contain property, which indicates that the element’s subtree is independent of the rest of the page. This enables heavy optimizations by user agents when used well.

This document is intended to become a W3C Recommendation. This
document will remain a Proposed Recommendation at least until 13 November 2019
in order to ensure the opportunity for wide review. The W3C
Membership and other interested parties are invited to review
the document and send comments. Advisory Committee Representatives
should respond to the corresponding WBS questionnaire:


Significant changes are listed at:


Disposition of comments:
Implementation Report:

The CSS WG has also published a First Public Working Draft of CSS Containment level 2:


This is initially identical to level 1 discussed above, except that it
retains an at-risk feature that was dropped from level 1 during the CR
period: style containment. This extends the concept—and benefits—of
containment to features like the counter-increment property or like
content:open-quote, which can otherwise have effects on more than just
an element and its descendants.

Please review the drafts, and send any comments to this mailing list,
<www-style@w3.org>, prefixed with [css-contain] (as I did on this
message) or (preferably) file them in the GitHub repository at

For the CSS WG,
—Florian Rivoal

Received on Tuesday, 15 October 2019 12:56:27 UTC