Apple’s File System Events API gives applications the ability to detect changes to paths containing relevant files recursively within an entire directory tree, both during execution and between launches. The File System Events API tackles the problem of detecting changes within a large chunk of the file system. A prime example of a use of this capability is Time Machine, which periodically launches and backs up any files modified since it last checked. Alternatively, this API could be used for syncing two directory trees on different machines over a network, or giving the user near-instant feedback about changes to specific files, for example in applications where many people collaborate on the same set of files.
