Even more nonsense possible since the tag function doesn't have to return a string, it can return a function, meaning you could chain these, e.g.

    function tag2(string, ...keys) {
      console.log("tag2", string, ...keys);
      return function tag1(string, ...keys) {
        console.log("tag1", string, ...keys);
        return "tag1-return-value"
      }
    }
    console.log(tag2`input to tag2``input to tag1`);

yields

    tag2 [ 'input to tag2' ]
    tag1 [ 'input to tag1' ]
    tag1-return-value