texmath-0.12.5: test/roundtrip/munder-10.native

[ EUnder False (EIdentifier "B") (EIdentifier "long under script")
, ESymbol Rel "="
, EUnder
    False
    (EGrouped
       [ EPhantom (EText TextNormal "x")
       , EIdentifier "B"
       , EPhantom (EText TextNormal "x")
       ])
    (EIdentifier "long under script")
]