[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.

[poncho_romero]

As they say in the article, your solution doesn’t work for even moderately complex layouts. If you want to add a space between elements, margin works wonderfully until those elements can wrap. Gap was introduced because regardless of what happens, there will always be a space between elements. Your solution fails to address the situation gap was introduced to fill.

[somishere]

Also doesn't really work when e.g. flex items are set to wrap

[micromacrofoot]

they aren't really edge cases, once you do this you add 1px to the layout unevenly - I run into this frustration with grid all the time

[madeofpalk]

Does this work in a grid?