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

<math xmlns="http://www.w3.org/1998/Math/MathML" display="block">  <munderover>    <mi mathvariant="normal">_ baseline _</mi>     <mphantom>      <mi mathvariant="normal">fail</mi>
    </mphantom>     <mphantom>      <mi mathvariant="normal">fail</mi>
    </mphantom>   </munderover>   <mo>=</mo>   <mi mathvariant="normal">_ baseline _</mi> </math>
>>> native
[ EUnderover
    False
    (EIdentifier "_ baseline _")
    (EPhantom (EIdentifier "fail"))
    (EPhantom (EIdentifier "fail"))
, ESymbol Rel "="
, EIdentifier "_ baseline _"
]