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# AVCaptureAncillaryDataUserKey

Clients may use an AVCaptureAncillaryDataUserKey to inspect the [`currentUserDefinedAncillaryData`](/documentation/AVFoundation/AVCaptureAncillaryDataEncoder/currentUserDefinedAncillaryData).

```
struct AVCaptureAncillaryDataUserKey
```

## Topics

### Creating a user key

[`init(rawValue: String)`](/documentation/AVFoundation/AVCaptureAncillaryDataUserKey/init(rawValue:))

### User key values

### Type Properties

[`static let rdd18InstanceUID: AVCaptureAncillaryDataUserKey`](/documentation/AVFoundation/AVCaptureAncillaryDataUserKey/rdd18InstanceUID)

An AVCaptureAncillaryDataEncoder key corresponding with the optional RDD18 user defined metadata Instance UID

[`static let rdd18UDAMSetVersion: AVCaptureAncillaryDataUserKey`](/documentation/AVFoundation/AVCaptureAncillaryDataUserKey/rdd18UDAMSetVersion)

An AVCaptureAncillaryDataEncoder key corresponding with the optional RDD18 user defined metadata UDAM Set Version

[`static let rdd18UserItems: AVCaptureAncillaryDataUserKey`](/documentation/AVFoundation/AVCaptureAncillaryDataUserKey/rdd18UserItems)

An AVCaptureAncillaryDataEncoder key corresponding with RDD18 user defined metadata

## Relationships

### Conforms To

[`Equatable`](/documentation/Swift/Equatable)

[`SendableMetatype`](/documentation/Swift/SendableMetatype)

[`Sendable`](/documentation/Swift/Sendable)

[`RawRepresentable`](/documentation/Swift/RawRepresentable)

[`Hashable`](/documentation/Swift/Hashable)

---

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