[CSSWG][css-position-3] Rewrote CSS Positioning Level 3

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


This module contains defines coordinate-based positioning and offsetting 
schemes of CSS: relative positioning, sticky positioning, absolute 
positioning, and fixed positioning.

This update completely rewrites the entire spec for editorial clarity, 
technical precision, and compatibility with [CSS-ALIGN-3] and 
[CSS-WRITING-MODES-3]. There should be no differences in behavior from CSS2.1, 
so please report any inconsistencies as errors. We've temporarily preserved 
some of the old abspos text as section 5, for comparison.

The definition of positioning containing blocks has been updated also to 
define two new terms: "absolute positioning containing block" and "fixed 
positioning containing block". These can be used by specs to more easily 
define when a particular property-value combination traps abspos or fixedpos 
elements. The term "containing block" as defined in CSS2.1 is now split across 
two specs:
     defines the fundamental concept
     defines the overriding behaviors triggered by positioning

We've also tightened up the description how margins are handled for stickypos 
to match implemented behavior, and defined behavior for overconstrained cases, 
closing off the issues previously annotated in that section.

This rewrite doesn't resolve all of the open issues against the spec, but we 
hope it forms a better foundation for future work.

Please review the draft, and send any comments to the www-style mailing list,
<www-style@w3.org>, prefixed with [css-position-3] (as I did on this
message) or (preferably) file them in the GitHub repository at

For the CSS WG,
~fantasai and Tab Atkins

Received on Tuesday, 19 May 2020 17:07:29 UTC