<<< native
[ EIdentifier "c"
, ESymbol Rel "="
, EOver
    False
    (EOver
       False
       (EGrouped
          [ EUnder
              False
              (EUnder False (EIdentifier "a") (ESymbol TUnder "\9183"))
              (EText TextNormal "real")
          , ESymbol Bin "+"
          , EUnder
              False
              (EUnder
                 False
                 (EGrouped
                    [ EIdentifier "b" , EStyled TextNormal [ EIdentifier "i" ] ])
                 (ESymbol TUnder "\9183"))
              (EText TextNormal "imaginary")
          ])
       (ESymbol TOver "\9182"))
    (EText TextNormal "complex number")
]
>>> tex
c = \overset{\text{complex number}}{\overbrace{\underset{\text{real}}{\underbrace{a}} + \underset{\text{imaginary}}{\underbrace{b\mathrm{i}}}}}