iframe

iframe, short for "inline frame", is the most common way that the allowfullscreen attribute is used. Thanks mostly to video sites like YouTube and Vimeo, videos embedded by third-party websites using an iframe can use the allowfullscreen attribute to enable a "fullscreen" button within the iframe.

Loading a YouTube Video via an iframe with the allowfullscreen attribute

Here is sample code for a YouTube video embedded using an iframe along with the allowfullscreen attribute:

<iframe width="560" height="315" src="//www.youtube.com/embed/jofNR_WkoCE" allowfullscreen></iframe>

When displayed in a browser, the iframe contains a fullscreen button:

Loading a Vimeo Video via an iframe with the allowfullscreen attribute

Here is another code example with a video embedded from Vimeo:

<iframe src="//player.vimeo.com/video/38514156" width="560" height="315" frameborder="0" allowfullscreen></iframe>

And, as before, when the iframe is displayed in a web browser, it looks like this: