Adding attributes to the <body>

When using `Browser.application` the view function should return a `Browser.Document`. A document like that lets you set the title and the html content of the `<body>` tag but not its attributes. And it seems that existing attributes on the `<body>`, before Gren is started, will be removed by Gren.

Is it possible somehow to have `<body class="hello">` when using `Browser.application`?