in public/javascripts/app/lib/box/index.js [8:16]
link: function(scope, el, attrs) {
//restrict the api so you can only use:
//<gu-box variant="primary"</gu-box>
//or
//<div gu-box="primary"</div>
var boxType = el[0].tagName === 'GU-BOX' ? attrs.variant : attrs.guBox;
var className = `box--${boxType}`;
el.addClass(className);
}