The following links trigger responses generated by the
service worker. There are two fetch handlers
registered in the service worker: the one that's registered first intercepts requests ending
with /hello/world and the one that's registered second intercepts requests that
contain /hello/ anywhere in their URL.
Since it's registered first, the handler which intercepts /hello/world requests
will always have the first chance to return a response via event.respondWith().
Only if the first handler doesn't call event.respondWith(), the second handler
gets its chance to call event.respondWith().
If none of the registered fetch handlers call event.respondWith(),
then the browser will handle the request by making a normal HTTP request, as if there were
no service worker involvement. This isn't an error condition, and it's a fine way
of ensuring that the default behavior is triggered.