Easy to access, well-supported in the Finder and elsewhere, Finder tags are powerful tools which rely on extended attributes to do their job. All you need to know about them.
tags
Why do the Open File and Save File dialogs normally behave differently with respect to tagged folders? It’s a question of semantics.
The Finder manages its tags, so changing the label of any tag is immediately reflected in all items using that tag. But what are null tags, and why are they so common?
Details of where and how files and folders store their Finder Tag information. One of the few xattrs intended for the user.
The Eclectic Light Company 