When the numbers simply don’t add up. How some extended attributes may be included in quoted file sizes, but others are ignored, and Sequoia hasn’t really changed this since Classic Mac OS of 25 years ago.
com.apple.ResourceFork
macOS has an elaborate set of rules determining which types of xattr are preserve during different types of copying, including syncing to iCloud Drive. Here they are in full detail.
Extended attributes were added to Mac OS X 10.4, and soon supported the quarantine xattr. They have since flourished, and have valuable properties.
How the resource forks of Classic Mac OS became extended attributes in Mac OS X 10.4, then flourished. How clone files handle xattrs, and which are used by APFS itself.
Why can’t other Macs and devices see custom folder and file icons in iCloud Drive? Why do some suddenly vanish?
The Eclectic Light Company 