What is the security model of iCloud Drive on iOS?
UIDocumentPickerViewController provides apps with open or import access to one or more user-specified files. Folders are not provided to apps for their own access to, and multiple selections must be user-initiated. When an app saves a file, it can retain access to that file but is not granted general access to the containing folder. Apps have access to their own app folders in iCloud Drive, but not the ability for any folder or all files.