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# allowedTopLevelClasses

A list of allowed classes the top-level object in an archive must conform to, for encoding and decoding.

```
class var allowedTopLevelClasses: [AnyClass] { get }
```

## Discussion

This property contains the value of [`transformedValueClass()`](/documentation/Foundation/ValueTransformer/transformedValueClass()) if that value isn’t `nil`. Otherwise, it holds a list of the top level classes that it decodes, which includes [`NSArray`](/documentation/Foundation/NSArray), [`NSDictionary`](/documentation/Foundation/NSDictionary), [`NSSet`](/documentation/Foundation/NSSet), [`NSString`](/documentation/Foundation/NSString), [`NSNumber`](/documentation/Foundation/NSNumber), [`NSDate`](/documentation/Foundation/NSDate), [`NSData`](/documentation/Foundation/NSData), [`NSURL`](/documentation/Foundation/NSURL), [`NSUUID`](/documentation/Foundation/NSUUID), and [`NSNull`](/documentation/Foundation/NSNull).

Override this property in subclasses to provide an expanded or different set of allowed transformation classes.

---

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