Huh! My Rust toy project (a simple “ls”) indicates whether a file has some xattrs. Unlike the real “ls”, my program shows a “+” sign if there is any xattr. The real “ls” only shows a “+” if ACL stuff is stored in those xattrs. And so, by accident, I found out that one of my files (so far) has an xattr called user.xdg.origin.url, which apparently shows the URL this file was downloaded from. 🤔