When the dom loads, a couple of IntersectionObserver are created, and the DOM is searched for elements with the class 'ad'. an IntersectionObserver is added to the div's found, which will start auctions with prebid.js if an ad is intersecting, or near intersecting the viewport. Another IntersectionObserver is used to fire some code when the ad comes fully into view. When the ad is rendered, a click handler is injected into the safe frame which allows us to run javascript if and when the ad is clicked.