Scripts and apps which could look at folders in iCloud should watch for stub files. Here’s how they work, and why they can mislead.
extended attributes
Its purpose is unknown, but it is automatically attached to contents of apps downloaded from iCloud Drive, if to a different system from the uploader.
How the two user modes differ, what iCloud Drive does to files transferred between two different clients, and an apparently unique tag it applies to apps which pass through.
Gatekeeper doesn’t seem interested in extended attributes attached to the contents of signed apps – the signature remains valid. Could this be exploited?
Sleeker, supports file drag and drop, with a very quick and simple way to add common metadata across many files.
How to use extended attributes and SearchKey to find the right file(s) first time, every time. Includes new beta-release.
Have you been warned not to use extended attributes because they aren’t supported beyond macOS? But they are: here are details of file systems and Cloud services.
New batch file mode can add (e.g.) copyright metadata to hundreds or thousands of files. Handles unusual characters properly. Can also remove extended attributes.
What metadata you are likely to encounter, where it is stored, and how you can view and edit it. A grand tour of the Finder’s Get Info dialog.
Adds keywords, author, copyright and other info to any file on your Mac. Runs in El Capitan, Sierra, and High Sierra.
The Eclectic Light Company 