  <p>
    <math>
      <mrow>
        <mspace width="1em" height="6em" style="background: blue"/>
        <mo id="percent_maxsize" maxsize="50%" stretchy="true" symmetric="false">⥯</mo>
        <mn><!-- not space like --></mn>
      </mrow>
    </math>
  </p>
  <p>
    <math>
      <mrow>
        <mspace width="1em" height=".5em" style="background: blue"/>
        <mo id="default_minsize" stretchy="true" symmetric="false">⥯</mo>
        <mn><!-- not space like --></mn>
      </mrow>
    </math>
  </p>
 