如何指定要在css flexbox中封装的元素?

I don't think this is part of the flexbox standard yet, but is there maybe a trick to suggest or force wrapping after a certain element? I'd like to respond to different page sizes and wrap a list differently without extra markup, so that rather than having (for example) orphaned menu items on the next line, I break in the middle of the menu.I don't think this is part of the flexbox stand