<<< native
[ EFraction
    NormalFrac
    (EIdentifier "A")
    (EGrouped
       [ EIdentifier "B"
       , ESymbol Bin "+"
       , EFraction
           NormalFrac
           (EIdentifier "C")
           (EGrouped
              [ EIdentifier "D"
              , ESymbol Bin "+"
              , EFraction NormalFrac (EIdentifier "E") (EIdentifier "F")
              ])
       ])
, ESymbol Rel "="
, EFraction
    NormalFrac
    (EOver False (EIdentifier "A") (EPhantom (ENumber "0")))
    (EGrouped
       [ EIdentifier "B"
       , ESymbol Bin "+"
       , EFraction
           NormalFrac
           (EIdentifier "C")
           (EGrouped
              [ EIdentifier "D"
              , ESymbol Bin "+"
              , EFraction
                  NormalFrac
                  (EIdentifier "E")
                  (EUnder False (EIdentifier "F") (EPhantom (ENumber "0")))
              ])
       ])
]
>>> tex
\frac{A}{B + \frac{C}{D + \frac{E}{F}}} = \frac{\overset{\phantom{0}}{A}}{B + \frac{C}{D + \frac{E}{\underset{\phantom{0}}{F}}}}