WordPress oEmbed W3C Validation

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The class-oembed.php file reveals some of the available filters regarding the oEmbeds.

We can use the oembed_result or oembed_dataparse filters to modify the HTML fetched from Vimeo before it’s cached in the post meta. Here’s an example for the latter:

add_filter( 'oembed_dataparse', function( $return, $data, $url )
{
    // Target only Vimeo:
    if(
            is_object( $data ) 
        &&  property_exists( $data, 'provider_name' )
        &&  'Vimeo' === $data->provider_name
    )
    {
        // Remove the unwanted attributes:
        $return = str_ireplace(
            array( 
                'frameborder="0"', 
                'webkitallowfullscreen', 
                'mozallowfullscreen' 
            ),
            '',
            $return
        );
    }
    return $return;
}, 10, 3 );

Example:

Before:

<iframe src="https://player.vimeo.com/video/32001208" 
        width="584" 
        height="329" 
        frameborder="0" 
        title="Earth" 
        webkitallowfullscreen 
        mozallowfullscreen 
        allowfullscreen></iframe>

After:

<iframe src="https://player.vimeo.com/video/32001208" 
        width="584" 
        height="329"  
        title="Earth"   
        allowfullscreen></iframe>

Additional notes on xhtml:

If you check out the Vimeo oEmbed API, there’s a xhtml parameter with the default xhtml=false. You can try for example:

https://vimeo.com/api/oembed.json?url=https%3A//vimeo.com/32001208

vs.

https://vimeo.com/api/oembed.json?url=https%3A//vimeo.com/32001208&xhtml=true

So instead of: 

webkitallowfullscreen mozallowfullscreen allowfullscreen

we get:

 webkitallowfullscreen="webkitallowfullscreen" 
 mozallowfullscreen="mozallowfullscreen" 
 allowfullscreen="allowfullscreen"

If we want to aim for XHTML validation, we could try to modify this via the oembed_remote_get_args, for example. But I didn’t test that.

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