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Re: [csswg-drafts] [css-overscroll-behavior] Interaction between overscroll-behavior and zooming (#3267)

From: Matt Rakow via GitHub <sysbot+gh@w3.org>
Date: Tue, 05 Feb 2019 16:54:58 +0000
To: public-css-archive@w3.org
Message-ID: <issue_comment.created-460715076-1549385697-sysbot+gh@w3.org>
The visual viewport (which carries the zoom and is the thing being scrolled in the normal chaining case) is associated with the root scroller.  Scroll chaining order doesn't change when zoomed vs. unzoomed, so if the chain is stopped prior to reaching the root (as it is by `#bugzilla-body` on your test page) it will prevent scrolling regardless of zoom.

The risk of a user manipulating themselves into a stuck state is not new to this feature, e.g. can occur when elements with `touch-action: none` or `ev.preventDefault()` are zoomed to cover the screen or inappropriately laid out.  This one is at least reversible by the user, since zooming back out should put them into a good state again.

A spec clarification on the visual viewport's participation and location in the chain would probably be good.  Maybe in [Scroll chaining and boundary default actions](https://drafts.csswg.org/css-overscroll-behavior/#scroll-chaining-and-boundary-default-actions), something like "The [visual viewport](https://wicg.github.io/visual-viewport) participates in chaining as the document's scrollingElement, both regarding placement in the chain as well as adhering to the chaining rules applied to it."

GitHub Notification of comment by ChumpChief
Please view or discuss this issue at https://github.com/w3c/csswg-drafts/issues/3267#issuecomment-460715076 using your GitHub account
Received on Tuesday, 5 February 2019 17:00:00 UTC

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