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# PreviewContextKey

A key type for a preview context.

```
protocol PreviewContextKey
```

## Overview

The default value is `nil`.

## Topics

### Setting a default

[`static var defaultValue: Self.Value`](/documentation/SwiftUI/PreviewContextKey/defaultValue)

The default value of the key.

[`associatedtype Value`](/documentation/SwiftUI/PreviewContextKey/Value)

The type of the value returned by the key.


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