<<< 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"
       ])
]
>>> tex
A\phantom{A}A + \frac{1 + 2 + 3}{1 + \phantom{2 +}3}