munder-12.test

<<< native
[ EUnder False (EIdentifier "B") (EIdentifier "underscript")
, ESymbol Rel "="
, EUnder
    False
    (EGrouped
       [ EPhantom (ENumber "1")
       , EIdentifier "B"
       , EPhantom (ENumber "1")
       ])
    (EIdentifier "underscript")
]
>>> tex
\underset{underscript}{B} = \underset{underscript}{\phantom{1}B\phantom{1}}