msubsup-05.test

<<< native
[ ESubsup
    (EIdentifier "S")
    (ESubsup (EIdentifier "Q") (ENumber "4") (ENumber "3"))
    (ESubsup (EIdentifier "P") (ENumber "2") (ENumber "1"))
, ESymbol Rel "="
, ESubsup
    (EIdentifier "S")
    (ESubsup
       (EIdentifier "Q")
       (EGrouped [ ENumber "4" , EPhantom (EText TextNormal "z") ])
       (ENumber "3"))
    (ESubsup
       (EIdentifier "P")
       (ENumber "2")
       (EGrouped [ ENumber "1" , EPhantom (EText TextNormal "z") ]))
]
>>> mml
<?xml version='1.0' ?>
<math display="block" xmlns="http://www.w3.org/1998/Math/MathML">
  <mrow>
    <msubsup>
      <mi>S</mi>
      <msubsup>
        <mi>Q</mi>
        <mn>4</mn>
        <mn>3</mn>
      </msubsup>
      <msubsup>
        <mi>P</mi>
        <mn>2</mn>
        <mn>1</mn>
      </msubsup>
    </msubsup>
    <mo>=</mo>
    <msubsup>
      <mi>S</mi>
      <msubsup>
        <mi>Q</mi>
        <mrow>
          <mn>4</mn>
          <mphantom>
            <mtext mathvariant="normal">z</mtext>
          </mphantom>
        </mrow>
        <mn>3</mn>
      </msubsup>
      <msubsup>
        <mi>P</mi>
        <mn>2</mn>
        <mrow>
          <mn>1</mn>
          <mphantom>
            <mtext mathvariant="normal">z</mtext>
          </mphantom>
        </mrow>
      </msubsup>
    </msubsup>
  </mrow>
</math>