- unstretched operators -->
        <mo stretchy="false">⥯</mo>
        <mo>+</mo>
        <mo>-</mo>
      </math>
      <math displaystyle="true">
        <!-- large operator -->
        <mo largeop="true">⥯</mo>
      </math>
      <math>
        <mrow>
          <!-- stretchy, small size -->
          <mspace height="2em"/>
          <mo>⥯</mo>
        </mrow>
      </math>
      <math>
        <mrow>
          <!-- stretchy, large size -->
          <mspace height="4em"/>
          <mo>⥯</mo>
 