Errors in W3 Validator

YouTube provides me with this code for embedding a video:

<iframe title=“YouTube video player” width=“640” height=“390” src=“” frameborder=“0” allowfullscreen></iframe>

I put the code in the W3 Validator and got this error: “allowFullScreen” is not a member of a group specified for any attribute

Why is this an error? I don’t understand why Google would give invalid code?

It is probably YouTube-specific code. As the error says allowFullScreen isn’t in the specs.

allowfullscreen is an attribute, much like title, src, but a custom one.

If xml was the subject here, then it could be possible to have custom attributes, custom elements.

In html world, this isn’t possible, you have a DTD which describes elements and their attributes. The validator uses this DTD and signals when aliens are spotted.

Yeah, don’t expect valid markup from Youtube – they pretty much crap all over the specification so badly it’s nothing short of a miracle their websites even work in the first place.

lol I guess I just have to work with what they give me.

The allowfullscreen custom attribute doesn’t appear to make a difference (at least not at the current time)? Remove it and you still get the ‘full screen’ option in the player.