lumn">
      <div>block1</div>
      <div class="spanner" style="display: flex;">flex as a spanner</div>
      <div>block2</div>
    </article>
    <br>

    <article class="column">
      <div>block1</div>
      <fieldset class="spanner">fieldset as a spanner</fieldset>
      <div>block2</div>
    </article>
    <br>

    <article class="column">
      <div>block1</div>
      <details open class="spanner">details as a spanner</details>
      <div>block2</div>
    </article>
    <br>

  </body>
</html>
