Spec Review for scroll-start-target

[DavMila]

こんにちは TAG-さん!

I'm requesting a TAG review of scroll-start-target

This is a proposal to introduce a CSS property which authors can use to control which element(s) a scroll container will be initially scrolled to, i.e. when it first appears on a page. It is intended to provide a reliable way for developers to give their scroll containers a non-(0,0) default starting scroll position without using JavaScript or other tricks involving animations and scroll-snapping.

• Explainer¹: https://github.com/DavMila/explainer-scroll-start-target
• Specification: https://drafts.csswg.org/css-scroll-snap-2/#scroll-start-target
• WPT Tests: https://wpt.fyi/results/css/css-scroll-snap-2/scroll-start-target?label=master&label=experimental&aligned
• User research: N/A
• Security and Privacy self-review²: This feature has no known privacy/security concerns.
• GitHub repo: https://github.com/w3c/csswg-drafts/blob/main/css-scroll-snap-2
• Primary contacts:
  • David Awogbemila (@DavMila, Google, Spec-writing)
  • Adam Argyle (@argyleink, Google, Spec-writing)
• Organization/project driving the specification: CSS Working Group
• Multi-stakeholder support³:
  • Chromium comments: Implemented as experimental feature: https://issues.chromium.org/u/1/issues/40909052
  • Mozilla comments: Mozilla Request
  • WebKit comments: WebKit Request
• Status/issue trackers for implementations⁴: chromestatus

Further details:

• [x] I have reviewed the TAG's Web Platform Design Principles
• Relevant time constraints or deadlines:
• The group where the work on this specification is currently being done: CSS Working Group
• The group where standardization of this work is intended to be done (if different from the current group):
• Major unresolved issues with or opposition to this specification: None

[jyasskin]

A couple questions here:

1. Is scroll-start-target: auto a developer-friendly way to say "please scroll to me"? I'd expect auto to mean "do what the UA thinks is right", which is not the behavior it's currently specified to have. I could imagine on-first-appearance being a clearer way to describe what it's asking for. This sort of naming question is firmly within the CSSWG's area of expertise, so there's probably a long discussion thread about it, and I would just benefit from a link to it.
2. https://drafts.csswg.org/css-scroll-snap-2/#scroll-start-target-fragment-navigation says "While the document is being updated ...". This sort of COMEFROM statement is out of favor in modern specifications. Can y'all work to add an appropriate hook in HTML?
3. If a page is slow to load and has multiple scroll-start-target elements, it seems like the current definition might cause multiple scrolls, if the UA decides to partially render after getting the initial target. Developers might not see this if they test only on a fast connection, but users on slower devices could wind up with a bad experience. Does something in the definition subtly prevent this? Has the WG discussed how to prevent it?

Thanks!