mrowAbg4

testing mathbackground color attribute

W3C sample	WIRIS
	$(x+x+x+x+x+x+x+x+x+x+x+x+x)$

<math xmlns="http://www.w3.org/1998/Math/MathML">
  <mstyle mathbackground="yellow">
    <mo>(</mo>
    <mi>x</mi>
    <mo>+</mo>
    <mi>x</mi>
    <mo>+</mo>
    <mi>x</mi>
    <mo>+</mo>
    <mi>x</mi>
    <mo>+</mo>
    <mi>x</mi>
    <mo>+</mo>
    <mi>x</mi>
    <mo>+</mo>
    <mi>x</mi>
    <mo>+</mo>
    <mi>x</mi>
    <mo>+</mo>
    <mi>x</mi>
    <mo>+</mo>
    <mi>x</mi>
    <mo>+</mo>
    <mi>x</mi>
    <mo>+</mo>
    <mi>x</mi>
    <mo>+</mo>
    <mi>x</mi>
    <mo>)</mo>
  </mstyle>
</math>

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