CSS Overflow for replaced elements

[khushalsagar]

Wotcher TAG!

I'm requesting a TAG review of CSS Overflow for replaced elements.

This feature allows developers to use the existing overflow property with replaced elements that paint outside the content-box. Paired with object-view-box this can be used to create an image with a custom glow or shadow applied, with proper ink-overflow behavior like a CSS shadow would have.

• Explainer¹ (minimally containing user needs and example code): https://github.com/WICG/shared-element-transitions/blob/main/overflow-on-replaced-elements.md, https://github.com/w3c/csswg-drafts/issues/7058.
• Specification URL: https://drafts.csswg.org/css-overflow/#propdef-overflow. See this issue for specific edits to this spec for this feature.
• Tests: WPTs are being added as part of implementation in Chromium.
• User research: N/A
• Security and Privacy self-review²: N/A. This change implements an existing CSS feature for replaced elements and doesn't introduce any new security/privacy concerns. One concern worth highlighting is allowing an iframe to generate ink overflow that can occlude content on the embedding frame. For this reason, a UA stylesheet enforces the overflow value to be clip for iframe, embed, object. See discussion here.
• GitHub repo (if you prefer feedback filed there): N/A
• Primary contacts (and their relationship to the specification):
  • Khushal Sagar (@khushalsagar), Google
  • Vladimir Levin (@vmpstr), Google
• Organization(s)/project(s) driving the specification: Google
• Key pieces of existing multi-stakeholder review or discussion of this specification:
• External status/issue trackers for this specification (publicly visible, e.g. Chrome Status): Chrome Status Entry

Further details:

• [X ] I have reviewed the TAG's Web Platform Design Principles
• Relevant time constraints or deadlines: N/A
• The group where the work on this specification is currently being done: WICG
• The group where standardization of this work is intended to be done (if current group is a community group or other incubation venue): CSSWG
• Major unresolved issues with or opposition to this specification: N/A
• This work is being funded by: Google

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]

[LeaVerou]

Hi there, We looked at this today during a breakout and it looks good to us. Thank you for flying TAG!

[khushalsagar]

Thanks for the review!