code: function genClassForVnode (vnode) {
    let data = vnode.data;
    let parentNode = vnode;
    let childNode = vnode;
    while (isDef(childNode.componentInstance)) {
      childNode = childNode.componentInstance._vnode;
      if (childNode && childNode.data) {
        data = mergeClassData(childNode.data, data);
      }
    }
    while (isDef(parentNode = parentNode.parent)) {
      if (parentNode && parentNode.data) {
        data = mergeClassData(data, parentNode.data);
      }
    }
    return renderClass(data.staticClass, data.class)
  }
docs: /*