texmath-0.12.5: test/roundtrip/msubsup-02.native

[ ESubsup
    (EGrouped [ EPhantom (EIdentifier "z") , EIdentifier "S" ])
    (EIdentifier "t")
    (ENumber "7")
, ESymbol Rel "="
, ESubsup (EIdentifier "S") (EIdentifier "t") (ENumber "7")
]