Where to look for file metadata in the Finder, and how you can customise it, in spite of its apparent confusion. And how APFS takes care of extended attributes for you.
xattr
Finder Comments are accessible, easy to use, and unreliable because they rely primarily on data stored in a hidden file. Regular Comment extended attributes are more reliable.
Extended attribute editor with much enhanced interface, app inspection tool, compression tool designed for AirDrop use, and a simple extended attribute editor for Spotlight search.
New version of this GUI utility for inspecting and editing extended attributes, for High Sierra and later.
How an obscure ACL can prevent a quarantine flag from being attached to an internet download: demonstration and explanation.
How the new tracking extended attribute is attached to apps, how it’s recorded in a security database, and how it’s checked. But for what purpose?
Ventura introduces a new extended attribute com.apple.provenance, used to mark successful clearance of quarantine. It’s protected by SIP too.
ResEdit changed what was in the resource fork. With Mac OS X, Apple moved away from forks to extended attributes, now used for quarantine flags and more.
Provided in Archive Utility and three command tools, its LZFSE compression even supports APFS special files like clones and sparse files.
Tired of HFS+? Disenchanted by APFS? Why not copy or back up to a different file system? Here are crocodiles waiting to bite you.
The Eclectic Light Company 