<<< native
[ EArray
    [ AlignCenter , AlignCenter , AlignCenter ]
    [ [ [ EOver
            False (EIdentifier "HT") (EPhantom (EText TextNormal "fail"))
        ]
      , [ ESymbol Rel "=" ]
      , [ EIdentifier "TH" ]
      ]
    ]
]
>>> tex
\begin{matrix}
\overset{\phantom{\text{fail}}}{HT} & = & {TH}
\end{matrix}