<<< native
[ EFraction
    NormalFrac
    (EGrouped
       [ EIdentifier "x"
       , ESymbol Bin "+"
       , EIdentifier "y"
       , ESymbol Bin "+"
       , EIdentifier "z"
       ])
    (EGrouped
       [ EIdentifier "x"
       , EPhantom (EGrouped [ ESymbol Bin "+" , EIdentifier "y" ])
       , ESymbol Bin "+"
       , EIdentifier "z"
       ])
]
>>> eqn
{x + y + z} over {x hphantom {+ y} + z}