Alerts and notifications
Users can sign up to receive an email notification when there is any change or a comment to any page (=node). You have to be signed in to sign up.
You can also subscribe to a page subgraph -- page and all of its descendant pages. This is a good way to stay updated on the developments withing a topic of the page and all of its subtopics represented by the descendant pages.
If you are subscribed to a page as a part of subgraph, at the top of the page you will see through which node you are subscribed.