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# fileWrapper(ofType:)

Creates and returns a file wrapper that contains the contents of the document, formatted to the specified type.

```
func fileWrapper(ofType typeName: String) throws -> FileWrapper
```

## Parameters

`typeName`

The string that identifies the document type.

## Return Value

A file wrapper containing the document contents, or, if the file wrapper could not be created, `nil`.

## Discussion

For backward binary compatibility with OS X v10.3 and earlier, if [`fileWrapperRepresentationOfType:`](/documentation/AppKit/NSDocument/fileWrapperRepresentationOfType:) is overridden, the default implementation of this method instead invokes `[self fileWrapperRepresentationOfType:typeName]`.

> Handling Errors in Swift:
> In Swift, this method is marked with the `throws` keyword to indicate that it throws an error in cases of failure.
> 
> When overriding this method, use the `throw` statement to throw an `NSError`, as described in [Error Handling](https://docs.swift.org/swift-book/LanguageGuide/ErrorHandling.html) in [The Swift Programming Language](https://docs.swift.org/swift-book/) and `About Imported Cocoa Error Parameters`.

---

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