code: function getRealChild (vnode) {
    const compOptions = vnode && vnode.componentOptions;
    if (compOptions && compOptions.Ctor.options.abstract) {
      return getRealChild(getFirstComponentChild(compOptions.children))
    } else {
      return vnode
    }
  }
docs: in case the child is also an abstract component, e.g. <keep-alive> we want to recursively retrieve the real component to be rendered