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# window(_:startCustomAnimationToEnterFullScreenWithDuration:)

This method is called to start the window animation into full-screen mode, including transitioning to a new space.

```
@MainActor optional func window(_ window: NSWindow, startCustomAnimationToEnterFullScreenWithDuration duration: TimeInterval)
```

## Parameters

`window`

The window to enter full-screen mode.

`duration`

The duration of the presentation change.

## Discussion

You can implement this method to perform custom animation with the given duration to be in sync with the system animation.

### Special Considerations

This method is called only if [`customWindowsToEnterFullScreen(for:)`](/documentation/AppKit/NSWindowDelegate/customWindowsToEnterFullScreen(for:)) returns non-`nil`.

---

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