row" stretchy="true">⥜</mo>
        <mo id="non_stretchy_horizontal_arrow" stretchy="false">⥚</mo>
        <mo id="non_stretchy_vertical_arrow" stretchy="false">⥜</mo>
      </mrow>
    </math>
  </p>
  <p>
    <math>
      <mrow>
        <!-- This contains only vertical stretchy operators. -->
        <mo style="font-size: 50%" id="small_vertical" stretchy="true">⥜</mo>
        <mo style="font-size: 200%" id="big_vertical" stretchy="true">⥜</mo>
        <mo style="font-size: 100%" id="medium_vert