The original source for the article is a bit clearer on what's actually happening, and the blog post for the HN link omits some details: https://eclecticlight.

The original source for the article is a bit clearer on what's actually happening, and the blog post for the HN link omits some details: https://eclecticlight.co/2018/01/06/icloud-drive-can-strip-metadata-from-your-documents/ https://eclecticlight.co/2018/01/06/icloud-drive-can-strip-m... I recommend read the original (and that the submission be changed to the original source instead), but a more accurate description here is that two Macs running two different versions of macOS will see the file differently once it's copied to iCloud. If a High Sierra Mac sends a file with a custom icon, for example, to iCloud, the High Sierra Mac will see the file as expected in iCloud. If a Mac on Sierra looks at the same file on the same iCloud share, it will see the base file without the custom icon. Other xattr items are removed as well, as documented in the original source.