mpadded15

W3C sample	WIRIS
	$x+\underline{x+y}+\underline{x+y}$

<math xmlns="http://www.w3.org/1998/Math/MathML">
  <mi>x</mi>
  <mo>+</mo>
  <munder>
    <mpadded depth="-10px">
      <mi>x</mi>
      <mo>+</mo>
      <mi>y</mi>
    </mpadded>
    <mo>&#x00332;</mo>
  </munder>
  <mo>+</mo>
  <munder>
    <mrow>
      <mi>x</mi>
      <mo>+</mo>
      <mi>y</mi>
    </mrow>
    <mo>&#x00332;</mo>
  </munder>
</math>

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