<<< native
[ EArray
    [ AlignCenter , AlignCenter , AlignCenter , AlignCenter ]
    [ [ [ EText TextNormal "Top" ]
      , [ ENumber "3" ]
      , [ EFraction
            NormalFrac
            (EGrouped [ EIdentifier "a" , ESymbol Bin "+" , ENumber "1" ])
            (ENumber "2")
        ]
      , [ EOver
            False
            (EIdentifier "y")
            (EFraction
               NormalFrac
               (EGrouped [ EIdentifier "a" , ESymbol Bin "+" , ENumber "1" ])
               (ENumber "2"))
        ]
      ]
    , [ [ EText TextNormal "Bottom" ]
      , [ ENumber "3" ]
      , [ EFraction
            NormalFrac
            (EGrouped [ EIdentifier "a" , ESymbol Bin "+" , ENumber "1" ])
            (ENumber "2")
        ]
      , [ EOver
            False
            (EIdentifier "y")
            (EFraction
               NormalFrac
               (EGrouped [ EIdentifier "a" , ESymbol Bin "+" , ENumber "1" ])
               (ENumber "2"))
        ]
      ]
    , [ [ EText TextNormal "Center" ]
      , [ ENumber "3" ]
      , [ EFraction
            NormalFrac
            (EGrouped [ EIdentifier "a" , ESymbol Bin "+" , ENumber "1" ])
            (ENumber "2")
        ]
      , [ EOver
            False
            (EIdentifier "y")
            (EFraction
               NormalFrac
               (EGrouped [ EIdentifier "a" , ESymbol Bin "+" , ENumber "1" ])
               (ENumber "2"))
        ]
      ]
    , [ [ EText TextNormal "Baseline" ]
      , [ ENumber "3" ]
      , [ EFraction
            NormalFrac
            (EGrouped [ EIdentifier "a" , ESymbol Bin "+" , ENumber "1" ])
            (ENumber "2")
        ]
      , [ EOver
            False
            (EIdentifier "y")
            (EFraction
               NormalFrac
               (EGrouped [ EIdentifier "a" , ESymbol Bin "+" , ENumber "1" ])
               (ENumber "2"))
        ]
      ]
    ]
]
>>> tex
\begin{matrix}
\text{Top} & 3 & \frac{a + 1}{2} & \overset{\frac{a + 1}{2}}{y} \\
\text{Bottom} & 3 & \frac{a + 1}{2} & \overset{\frac{a + 1}{2}}{y} \\
\text{Center} & 3 & \frac{a + 1}{2} & \overset{\frac{a + 1}{2}}{y} \\
\text{Baseline} & 3 & \frac{a + 1}{2} & \overset{\frac{a + 1}{2}}{y}
\end{matrix}