msubsup-01.test

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

<math xmlns="http://www.w3.org/1998/Math/MathML" display="block">  <msubsup>    <mi>R</mi>     <mn>0</mn>     <mn>4</mn>   </msubsup>   <mo>=</mo>   <msubsup>    <mi>R</mi>     <mrow>      <mn>0</mn>
      <mphantom>
        <mi>fail</mi>
      </mphantom>
    </mrow>     <mrow>      <mn>4</mn>
      <mphantom>
        <mi>fail</mi>
      </mphantom>
    </mrow>   </msubsup> </math>
>>> native
[ ESubsup (EIdentifier "R") (ENumber "0") (ENumber "4")
, ESymbol Rel "="
, ESubsup
    (EIdentifier "R")
    (EGrouped [ ENumber "0" , EPhantom (EIdentifier "fail") ])
    (EGrouped [ ENumber "4" , EPhantom (EIdentifier "fail") ])
]