element sets displaystyle to "false", or if it was already
         false increments scriptlevel by 1, within numerator and denominator.
      -->
    <math>
      <mstyle displaystyle="true">
        <mfrac>
          <msub><mo>O</mo><mo>O</mo></msub>
          <msub><mo>O</mo><mo>O</mo></msub>
        </mfrac>
      </mstyle>
    </math>

    <!--    The mroot element increments scriptlevel by 2, and sets
            displaystyle to "false", within index, but leaves both attributes
            unchanged w