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# URL session error dictionary keys

Keys used in conjunction with error objects returned by URL sessions and tasks.

## Topics

### User info dictionary keys

[`let NSURLSessionDownloadTaskResumeData: String`](/documentation/Foundation/NSURLSessionDownloadTaskResumeData)

A key in the error dictionary that provides resume data.

[`let NSURLErrorBackgroundTaskCancelledReasonKey: String`](/documentation/Foundation/NSURLErrorBackgroundTaskCancelledReasonKey)

A key in the error dictionary that provides the reason for canceling a background task.


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