Information about the data in a file can be found in different places: in the file’s attributes, in extended attributes that tend to be Mac-only, and embedded with the data, as in EXIF.
resource
From the resource forks of Classic apps, to versioned and new-style bundles in 2001, document packages, then the incorporation of signatures and notarization tickets.
Adding your own custom icons to files and folders goes back a long way, to Classic Mac OS […]
From the original Desktop databases linking files to distinctive icons, to the sophistication of QuickLook, how display of thumbnails for files has changed in Mac OS.
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.
Classic Mac OS stored a great deal of structured data in the resource forks of its files. Those were edited using ResEdit, an essential tool for every advanced user.
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 are some file metadata embedded in their main data, and others stored separately as extended attributes? How can I tell them apart?
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 