Formatting of right hand side of equation should be identical to formatting of left hand side
<math xmlns="http://www.w3.org/1998/Math/MathML" display="block">
  <msup>
    <mi>x</mi>
    <mn>3</mn>
  </msup>
  <mo>=</mo>
  <msup>
    <mrow>
      <mi>x</mi>
    </mrow>
    <mrow>
      <mn>3</mn>
    </mrow>
  </msup>
</math>
Author: George Chavchanidze, Opera Software ASA