<math xmlns="http://www.w3.org/1998/Math/MathML">
<mfrac>
<mn>1</mn>
<mn>2</mn>
</mfrac>
<mo>+</mo>
<mstyle mathbackground="yellow">
<mpadded depth="+10px">
<mi>x</mi>
<mo>+</mo>
<mi>y</mi>
</mpadded>
</mstyle>
<mo>+</mo>
<mi>x</mi>
</math>
Author: Design Science, Inc. (D. Doyle, E. Cannon, E. Tabacman, R.Miner)