The optimal block size to use when reading or writing this file's data, returned as an
NSNumber object, or
nil if the preferred size is not available (read-only).
- iOS 5.0+
- macOS 10.7+
- Mac Catalyst 13.0+
- tvOS 9.0+
- watchOS 2.0+
static let isPackageKey: URLResourceKey
Key for determining whether the resource is a file package, returned as a Boolean
NSNumber object (read-write in macOS 10.8 and later, read-only in previous versions). A
true value means that the resource is a file package.