[w3ctag/design-reviews] CSS Overflow for replaced elements (Issue #750)

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](https://github.com/w3c/csswg-drafts/issues/7144) 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](https://github.com/w3c/csswg-drafts/issues/7143).
  - 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): https://chromestatus.com/guide/edit/5137515594383360


Further details:

  - [X ] I have reviewed the TAG's [Web Platform Design Principles](https://www.w3.org/TR/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]


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