Manual testing is crucial. And therefore, reducing friction to let you start your testing process can be a huge help. Selecting some accessibility shortcuts will do that, putting most of iOS' accessibility features at a triple-click of a button.
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You can add an observer to listen for changes in the content size category, in case it is more convenient than overriding traitCollectionDidChange(_:).
When implementing a UISlider, it is a good idea to consider how much the slider value should change when swiping up/down to adjust it. It might not always make sense to do it in 10% increments, which is the default behaviour. Could be because the value at those intervals doesn't make sense, or feel random, or because it wouldn't provide the user with a fine enough control being able to go through the whole slider in just 10 swipes. It user will still be able to adjust the slider to any value by double tapping and holding and then moving the finger left or right, bypassing VoiceOver gestures. VoiceOver announces the new value as it changes.
Since iOS 14, you can get a human readable localised name for a UIColor, with a very useful property called accessibilityName, that you can use in accessibility attributes like labels or values. How cool is that? https://developer.apple.com/documentation/uikit/uicolor/accessibilityname
