The validator isn't up to date, then.
https://html.spec.whatwg.org/multipage/embedded-content.html#attr-iframe-allowfullscreen
However it should be just allowfullscreen
, not allowfullscreen="true"
.
https://validator.nu/ supports the allowfullscreen
attribute.
Without the attribute, native fullscreen with requestFullscreen()
will not work. Fullscreen from Flash or so might still work. I don't know what vimeo does but possibly it uses <video>
+ requestFullscreen()
for some users or will do so in the future.
https://fullscreen.spec.whatwg.org/#dom-element-requestfullscreen