> I'm really surprised that this sort of functionality isn't built into OS's/filesystems
It appears to be built into macOS [1]?
> Whenever the filesystem is changed, the kernel passes notifications via the special device file /dev/fsevents to a userspace process called fseventsd
Which I assume is what they're referring to here:
> A platform filesystem watcher for Darwin is used, but certain event properties are handled by the standard library. Namely, the event time and the path type.