docs: function findQualifiedChildren (instance) {
    return isQualified(instance)
      ? capture(instance)
      : findQualifiedChildrenFromList(instance.$children).concat(
        instance._vnode && instance._vnode.children
          // Find functional components in recursively in non-functional vnodes.
          ? flatten(instance._vnode.children.filter(child => !child.componentInstance).map(captureChild))
            // Filter qualified children.
            .filter(instance => isQualified(instance))
          : []
      )
  }