Extended attributes were added to Mac OS X 10.4, and soon supported the quarantine xattr. They have since flourished, and have valuable properties.
metadata
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.
Version 1.5 of this metadata editor fixes a bug causing a spurious editor when Autosave is enabled.
The most accessible of any metadata in the Finder and apps, Finder tags can be ideal for classifying files and folders into no more than 7 categories. Here’s how they work.
Fixes one bug, and adds two new features. Can now autosave, to help you make workflows quicker and more reliable.
Version 1.3 adds drag and drop onto a document window, and a Scratchpad to store keywords that you use often. For 10.14.6 and later.
Why are some file metadata embedded in their main data, and others stored separately as extended attributes? How can I tell them apart?
Second beta adds support for all metadata keys, has an extensive Help book, and saves results in a text file. Discover the keywords you can search for.
Automated image analysis and other tools store keywords in many different types of files. To search effectively for keywords, though, you need to know which terms have been used.
It can take many hours for files to be downloaded from iCloud. Apps must be able to cope with that, but how well does macOS?
The Eclectic Light Company 