[cpearce]

Your video fallback behaviour seems superfluous. If you want fullscreen on a video, why don't you just request fullscreen on the video rather than its container?

Having the fullscreen request shift to the descendent video also breaks the case where you actually have an element containing a video that you want to make fullscreen, for example if you have custom controls for your video element... This is simply impossible with your API.

[bdougherty]

If you have custom controls, putting that element in full screen will work if the browser you're in (and/or the iframe you're in) supports the newer fullscreen API.

It only falls back in the case where that doesn't work (older browser, no allowfullscreen attribute on the iframe) and supports the older API that is just for video tags.