mphantomBoperators3

W3C sample	WIRIS
	$A+A\phantom{+}A$

<math xmlns="http://www.w3.org/1998/Math/MathML">
  <mrow>
    <mi>A</mi>
    <mo>+</mo>
    <mi>A</mi>
    <mphantom>
      <mo>+</mo>
    </mphantom>
    <mi>A</mi>
  </mrow>
</math>

Author: Robert Miner and Jeff Schaefer, Geometry Technologies