<!doctype html>
<html>
  <head>
    <title>base alignment</title>
    <meta charset="utf-8"/>
  </head>
  <body>

    <!-- The bases of the outermost <mmultiscripts> elements should all be aligned and so covered by the blue rectangle. -->
    <p style="position: absolute;">
      <math>
        <mspace height="10em" depth="10em"/>
        <mn>0</mn>
        <msup><mn>0</mn><mn>1</mn></msup>
        <msub><mn>0</mn><mn>1</mn></msub>
        <msubsup><mn>0</mn><mn>1</mn><mn>2</mn></msubsup>
        <mmultiscripts><mn>0</mn><mn>1</mn><mn>2</mn><mn>3</mn><mn>4</mn><mprescripts/><mn>5</mn><mn>6</mn><mn>7</mn><mn>8</mn></mmultiscripts>

        <mmultiscripts>
          <mn>0</mn>
          <mmultiscripts><mn>1</mn><mn>2</mn><none/></mmultiscripts>
          <none/>
        </mmultiscripts>
        <mmultiscripts>
          <mn>0</mn>
          <none/>
          <mmultiscripts><mn>1</mn><none/><mn>2</mn></mmultiscripts>
        </mmultiscripts>
        <mmultiscripts>
          <mn>0</mn>
          <mprescripts/>
          <mmultiscripts><mn>1</mn><mprescripts/><mn>2</mn><none/></mmultiscripts>
          <none/>
        </mmultiscripts>
        <mmultiscripts>
          <mn>0</mn>
          <mprescripts/>
          <none/>
          <mmultiscripts><mn>1</mn><mprescripts/><none/><mn>2</mn></mmultiscripts>
        </mmultiscripts>

        <mmultiscripts>
          <mn>0</mn>
          <mmultiscripts>
            <mn>0</mn>
            <mn>1</mn><mn>2</mn>
            <mn>3</mn><mn>4</mn>
            <mprescripts/>
            <mn>5</mn><mn>6</mn>
            <mn>7</mn><mn>8</mn>
          </mmultiscripts>
          <mmultiscripts>
            <mn>0</mn>
            <mn>1</mn><mn>2</mn>
            <mn>3</mn><mn>4</mn>
            <mprescripts/>
            <mn>5</mn><mn>6</mn>
            <mn>7</mn><mn>8</mn>
          </mmultiscripts>
          <mprescripts/>
          <mmultiscripts>
            <mn>0</mn>
            <mn>1</mn><mn>2</mn>
            <mn>3</mn><mn>4</mn>
            <mprescripts/>
            <mn>5</mn><mn>6</mn>
            <mn>7</mn><mn>8</mn>
          </mmultiscripts>
          <mmultiscripts>
            <mn>0</mn>
            <mn>1</mn><mn>2</mn>
            <mn>3</mn><mn>4</mn>
            <mprescripts/>
            <mn>5</mn><mn>6</mn>
            <mn>7</mn><mn>8</mn>
          </mmultiscripts>
        </mmultiscripts>
      </math>
    </p>

    <p style="position: absolute;">
      <math>
        <mspace height="10em" depth="10em"/>
        <mrow mathbackground="blue" style="border-top: blue solid 1px; border-bottom: blue solid 1px;">
          <mphantom>
            <mn>0000000000000000000000000000000000000000000</mn>
          </mphantom>
        </mrow>
      </math>
    </p>

  </body>
</html>
