The title of the HTML anchor link for the <box> CSS type is:

Expands to: border-box | content-box | fill-box | margin-box | padding-box | stroke-box | svg viewport origin box | view-box

But it is defined with border-box | padding-box | content-box.

I am not sure how it is generated. I cannot find svg viewport origin box in any CSS spec. I guess it is a caching issue.