-Emitted when the process is about to exit. This is a good hook to perform
-constant time checks of the module's state (like for unit tests). The main
-event loop will no longer be run after the 'exit' callback finishes, so
-timers may not be scheduled.
+Emitted when the process is about to exit. There is no way to prevent the
+exiting of the event loop at this point, and once all `exit` listeners have
+finished running the process will exit. Therefore you **must** only perform
+**synchronous** operations in this handler. This is a good hook to perform
+checks on the module's state (like for unit tests). The callback takes one
+argument, the code the process is exiting with.