ise be scoped:
       e.g. :host ::content > .bar -> x-foo > .bar

     * ::shadow, /deep/: processed simimlar to ::content

     * :host-context(...): NOT SUPPORTED

    */

    // Given a node and scope name, add a scoping class to each node 
    // in the tree. This facilitates transforming css into scoped rules. 
    function transformDom(node, scope, useAttr, shouldRemoveScope) {
      _transformDom(node, scope || '', useAttr, shouldRemoveScope);
    }

    function _transformDom(node, s