Suggested approach: This is used to blur backgrounds, either light or dark, so that text can be overlaid more easily. You can optionally enable vibrancy, which causes the text to be rendered in a bright, contrasting color alongside the blur.
Of course, the real underlying question here is why they exist at all, and here you'll probably want to talk about keeping parts of your UI visible, even when it's just blurred, to help provide some extra context to your user of where they are in your app.
Estimated difficulty: Easy
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