If you have Optimise Mac Storage enabled for iCloud Drive, this new feature lets you pin the files you want to be stored locally and not evicted. Full details.
xattr
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.
It has often been assumed that App Store apps don’t undergo app translocation. That isn’t true: here’s an example of one that gets stuck in eternal translocation because it comes with an unwanted gift.
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.
Understanding how APFS works: inodes, attributes, file extents, extended attributes, and how they change with editing and cloning.
Step by step through moving to iCloud Drive, eviction to a dataless file, materialisation of local data, editing and syncing with iCloud Drive.
How local files retain their extended attributes and versions when moved to iCloud Drive, but they’re not available to other Macs. Sparse files and storage economy as well.
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.
The Eclectic Light Company 