mpadded14

W3C sample WIRIS
1 2 + x + y ¯ + x + y ¯ 
<math xmlns="http://www.w3.org/1998/Math/MathML">
  <mfrac>
    <mn>1</mn>
    <mn>2</mn>
  </mfrac>
  <mo>+</mo>
  <mover>
    <mpadded height="-10px">
      <mi>x</mi>
      <mo>+</mo>
      <mi>y</mi>
    </mpadded>
    <mo>&#x000AF;</mo>
  </mover>
  <mo>+</mo>
  <mover>
    <mrow>
      <mi>x</mi>
      <mo>+</mo>
      <mi>y</mi>
    </mrow>
    <mo>&#x000AF;</mo>
  </mover>
</math>

Author: Design Science, Inc. (D. Doyle, E. Cannon, E. Tabacman, R.Miner)