msub-11.test

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

<math xmlns="http://www.w3.org/1998/Math/MathML" display="block">  <msub>    <mi mathvariant="normal">H</mi>     <mo>2</mo>   </msub>   <mo>=</mo>   <mover>    <mrow>      <msub>        <mi mathvariant="normal">H</mi>         <mo>2</mo>       </msub>     </mrow>     <mphantom>      <mi>x</mi>
    </mphantom>   </mover> </math>
>>> native
[ ESub (EIdentifier "H") (ESymbol Ord "2")
, ESymbol Rel "="
, EOver
    False
    (ESub (EIdentifier "H") (ESymbol Ord "2"))
    (EPhantom (EIdentifier "x"))
]