Change Detection 应用
Change Detection tracks changes on websites you otherwise would visitfrequently to see if there is something new. Use cases:
* Teacher says grades will be published "soon", but no one knows what "soon" means and you are tired of reloading.
* You are working with a server and wants to know the result from a request, periodically.
* You are waiting for updates on an Exam, like if something was postponed or updated.
* You want to monitor the Dagger documentation to see when Thermosiphon's explanation improves.
