Clojurians Log v2

Can someone please explain to me how r/atom s are implemented? It's my understanding that when a component using a r/atom is rendered, deref s are recorded, so Reagent "knows" which component depends on which r/atom s. I assume that when a r/atom 's value is then modified, Reagent "knows" that the depending components should be re-rendered. How is that triggered? It's my understanding that usually React components are re-rendered when either their properties changes or their .setState is called (or something like that). So what does Reagent do to trigger the re-rendering -- one of the above, something else?

Or does Reagent call something like .forceUpdate ?