<<< native
[ EUnderover
    False
    (EIdentifier "- middle -")
    (EPhantom (EIdentifier "fail"))
    (EIdentifier "top")
, ESymbol Rel "="
, EOver False (EIdentifier "- middle -") (EIdentifier "top")
]
>>> tex
\underset{\phantom{fail}}{\overset{top}{-\ middle\ -}} = \overset{top}{-\ middle\ -}