This test checks which elements have [[Prototype]] referencing "generic" HTMLElement and which ones don't. I was curious whether elements introduced in HTML5 implement "specific" interfaces (such as HTMLDivElement, HTMLSpanElement, etc.). For example, I noticed that some browsers that don't support VIDEO element, set that element's [[Prototype]] to generic HTMLElement, but those that do — to HTMLVideoElement. This is by far not the best indication of certain element being "supported", since many browsers give even some of the long-supported HTML4 elements (e.g. dd, dt, em, strong, etc.) [[Prototype]] of HTMLElement. However, it's still interesting to see what [[Prototype]]'s of various elements are.