Comment by Pikamander2

It's a decent idea, but it feels like it would have been more useful a decade ago.

With modern CSS you can typically handle separators with a single selector and property like:

  .things .thing:not(:last-child)
  {
      border-bottom: 1px solid gray;
  }

They touch on this in the article but I feel like they're overselling the frequency of edge cases.