Image:

Your browser's rendering:

1 2 x y

Source Code:

    <math>
      <mtable frame="dashed" framespacing="0.4em 0.5ex">
        <mtr>
          <mtd>
            <mn>1</mn>
          </mtd>
          <mtd>
            <mn>2</mn>
          </mtd>
        </mtr>
        <mtr>
          <mtd>
            <mi>x</mi>
          </mtd>
          <mtd>
            <mi>y</mi>
          </mtd>
        </mtr> 
      </mtable>
    </math>