<<< native
[ EText TextNormal "Inline, auto, thick line\160"
, EFraction
    NormalFrac
    (EGrouped
       [ ESuper (EIdentifier "x") (ENumber "2")
       , ESymbol Bin "+"
       , ENumber "1"
       ])
    (EIdentifier "x")
, EText
    TextNormal ", the superscripted 2 should be script-script size."
]
>>> tex
\text{Inline, auto, thick line~}\frac{x^{2} + 1}{x}\text{, the superscripted 2 should be script-script size.}