[Webkit-unassigned] [Bug 254205] New: AX: iOS VoiceOver skips newly rendered Web DOM elements

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=254205

            Bug ID: 254205
           Summary: AX: iOS VoiceOver skips newly rendered Web DOM
                    elements
           Product: WebKit
           Version: Safari 16
          Hardware: iPhone / iPad
                OS: iOS 16
            Status: NEW
          Severity: Critical
          Priority: P2
         Component: UI Events
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: gintaras.grazinskis1 at usbank.com

Created attachment 465537

  --> https://bugs.webkit.org/attachment.cgi?id=465537&action=review

Bug reproduction on iPad

VoiceOver sometimes cannot “see” newly rendered elements. This can happen with or without user interaction. For example: virtualized list that renders new elements as user scrolls; some status page that updates DOM based on Ajax polling. 

Steps to reproduce:
1. Open https://suex2z.csb.app/ on an iOS device;
2. Turn on VoiceOver;
3. Click button “0”;
4. App will render four new buttons: 1, 2, 3, 4 with one second delay between each render;
5. Before “4” is rendered, swipe right to navigate to the next button;
6. After “4” is rendered, try to navigate onto “4” by swiping right.

Expected result: VO focus shifts to button “4”.

Actual result: VO focus goes to “Open sandbox” button. Last focused button is 1, 2 or 3. But never “4”. "4" was skipped.

While this example might look like an edge case, such bug can occur with list virtualization. For example, we’ve encountered this behaviour with the library https://virtuoso.dev/.

Is this behaviour documented somewhere? We were not able to find information on this online.

Devices where we were able to reproduce this: iPad 9th gen (iOS 15.6), iPhone 11 (iOS 16.02).

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