UIDocumentPickerViewController: open to specific folder

Hi, With UIDocumentPickerViewController, there is a directoryURL property that says we can use to 'specify the starting directory for the document picker'. But it's not clear how to get the directory of a folder in iCloud Drive / Files app. How can I get the 'root' directory for a user's iCloud Drive or Dropbox folder, or the Downloads folder on their device, that I could pass to this directoryURL to make it easier for the user to pick their files? Thanks.

UIDocumentPickerViewController: open to specific folder
 
 
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