texmath-0.12.5: test/roundtrip/msup-12.native

[ ESuper (EIdentifier "a") (ESymbol Bin "+")
, ESymbol Rel "="
, EUnderover
    False
    (ESuper (EIdentifier "a") (ESymbol Bin "+"))
    (EPhantom (EIdentifier "x"))
    (EPhantom (EIdentifier "x"))
]