When presenting a UI component that overlays the existing UI, you may have found that VoiceOver starts to randomly jump between the overlaid UI and the elements underneath. To avoid that, you can set its accessibilityViewIsModal to true.
When setting the accessibilityViewIsModal to true for a view, VoiceOver will ignore its sibling views, treating it as if it was a modal. Useful when presenting custom popups, popovers, modals, action sheets, etc.
https://developer.apple.com/documentation/objectivec/nsobject-swift.class/accessibilityviewismodal
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If you want to know everything about how to "Tailor the VoiceOver experience in your data-rich apps" with the Accessibility Custom Content API, there is a WWDC21 session. https://developer.apple.com/videos/play/wwdc2021/10121/ When implementing accessibilityCustomContent, for any supplementary information, it returns an array that VoiceOver will announce in that given order. The value of the AXCustomContent first, then the label. Users can configure in VoiceOver's verbosity settings if it should say that there's more content available, or play a sound hinting that there is, or simply do nothing. So it should really be optional content as users might miss it.
Have you ever seen VoiceOver randomly focusing on elements of the previous view when presenting a custom modal view? That can be fixed by letting the system know that the presented view is modal in terms of accessibility.
You should convey important information in multiple modes, not just color. If you are still required to do so, at the very least you should complement that info with other modes, like symbols, if the user requested differentiation without color.
