<<< native
[ EIdentifier "A"
, EPhantom (EIdentifier "A")
, EIdentifier "A"
, ESymbol Bin "+"
, EFraction
    NormalFrac
    (EGrouped
       [ ENumber "1"
       , ESymbol Bin "+"
       , ENumber "2"
       , ESymbol Bin "+"
       , ENumber "3"
       ])
    (EGrouped
       [ ENumber "1"
       , ESymbol Bin "+"
       , EPhantom (EGrouped [ ENumber "2" , ESymbol Bin "+" ])
       , ENumber "3"
       ])
]
>>> eqn
A hphantom A A + {1 + 2 + 3} over {1 + hphantom {2 +} 3}