It is a simple innovation. It was an ad for a Chinese university and I saw it on the Economist website.
Here’s what they did - they put a scroll within the square display ad. The text was larger than the size of the ad so you could scroll and read the entire text using a scroll bar within the ad. Which means that if you want, you can fit in the entire contents of a website in that small square ad… wow!
By the way when I went back to look for it on the Economist website I couldn't find it again. If any of you come across the ad (ugly and inconspicuous but unmissable placement on the right side) please share a link in the comments.Follow my blog with Bloglovin