Expected behavior of background-clip property on the html element?

 What is the expected behavior when the background-clip property is applied to the html element. For instance:

        html
        {
                border:15px dashed #354658;
                padding: 30px;
                background-color: green;
                background-clip: border-box;
        }

Should the green color stop at the outer edges of the dashed border? How about when background-clip is padding-box or content-box?

When I try this on the major browsers, all show the green background well beyond the bottom border. Additionally, content-box behaves exactly the same as either border-box (Chrome, FF, Safari) or padding-box (Opera). Which is correct? I'm guessing neither, but it's not immediately clear from the spec.

Thanks.

Regards, Cathy.