docs: function(type, callback) {
        var isSupported = false,
        root = document.documentElement,
        div = document.createElement('div'),
        handler = function() { isSupported = true; };
        root.insertBefore(div, root.firstChild);
        div.addEventListener(type, handler, true);
        if (callback && callback.call) callback(div);
        div.removeEventListener(type, handler, true);
        root.removeChild(div);
        return isSupported;
      }