e: accent was a shared attribute name for mover and mo, so
           make mstyle an ancestor of mo but not of mover. -->
      <mover>
        <mn>4</mn>
        <mstyle accent="false"><mo>⇀</mo></mstyle>
      </mover>
      <mstyle stretchy="false" symmetric="false" maxsize="20px">
        <mrow>
          <mo>|</mo>
          <mspace height="100px"></mspace>
        </mrow>
      </mstyle>
      <mstyle minsize="100px">
        <mrow>
          <mo>|</mo>
          <mn>4</mn>
        </mrow>
      </m