I recall an anecdote about a mathematician being asked to clarify precisely what he meant by “a close approximation to three”. After thinking for a moment, he replied “any real number other than three”.

Are you using the standard xattr command that’s built into macOS? IIRC there’s another program out there by the same name with completely different syntax. Try running type xattr; it should say something like “xattr is /usr/bin/xattr” if you’re using the standard one.