Foldable Device CSS Primitives #690

Braw mornin' TAG!

I'm requesting a TAG review of Foldable Device CSS Primitives after taking into account feedback (w3c/csswg-drafts#5621 and w3c/csswg-drafts#5622) on our original Foldables CSS proposal (initial TAG review here: #472)

In order to enable web developers to build layouts that are optimized for foldable experiences declaratively using CSS, we must consider fundamental assumptions of CSS (i.e. a single contiguous rectangular space for laying out content) and introduce new primitives that -together with existing layout media queries- allow developers to create layouts that react to states where the root viewport spans multiple displays.

• Explainer¹ (minimally containing user needs and example code): https://github.com/MicrosoftEdge/MSEdgeExplainers/blob/main/Foldables/explainer.md
• Specification URLs:
  • Media Queries: https://drafts.csswg.org/mediaqueries-5/#mf-horizontal-viewport-segments
  • Environment Variables: https://drafts.csswg.org/css-env-1/#viewport-segments
• Tests: https://wpt.fyi/results/css/css-env/indexed-env.tentative.html
• Security and Privacy self-review²: [Foldable] CSS - TAG Security and Privacy questionnaire MicrosoftEdge/MSEdgeExplainers#187
• GitHub repo (if you prefer feedback filed there):
• Primary contacts (and their relationship to the specification):
  • Daniel Libby, @dlibby-, Microsoft
  • Stephanie Stimac, @ststimac, Microsoft
  • Scott Low, @scottlow, Microsoft
• Organization/project driving the design: Microsoft
• External status/issue trackers for this feature (publicly visible, e.g. Chrome Status):

Further details:

• I have reviewed the TAG's Web Platform Design Principles
• The group where the work on this specification is currently being done: CSSWG
• Major unresolved issues with or opposition to this specification: N/A
• This work is being funded by: Microsoft

We'd prefer the TAG provide feedback as (please delete all but the desired option):

💬 leave review feedback as a comment in this issue and @-notify [github usernames]