msubsup-01.test

<<< native
[ ESubsup (EIdentifier "R") (ENumber "0") (ENumber "4")
, ESymbol Rel "="
, ESubsup
    (EIdentifier "R")
    (EGrouped [ ENumber "0" , EPhantom (EIdentifier "fail") ])
    (EGrouped [ ENumber "4" , EPhantom (EIdentifier "fail") ])
]
>>> eqn
R sub 0 sup 4 = R sub {0 hphantom fail} sup {4 hphantom fail}