<<< mml
<?xml version="1.0" encoding="UTF-8"?>

<math xmlns="http://www.w3.org/1998/Math/MathML" display="block">  <msup>    <mi>a</mi>     <mn>2</mn>   </msup>   <mo>=</mo>   <msup>    <mi>a</mi>     <mrow>      <mover>        <mn>2</mn>
        <mphantom>
          <mi>x</mi>
        </mphantom>
      </mover>
    </mrow>   </msup> </math>
>>> native
[ ESuper (EIdentifier "a") (ENumber "2")
, ESymbol Rel "="
, ESuper
    (EIdentifier "a")
    (EOver False (ENumber "2") (EPhantom (EIdentifier "x")))
]