<<< native
[ ESqrt (EIdentifier "content")
, ESymbol Rel "="
, ESqrt
    (EUnder
       False (EIdentifier "content") (EPhantom (EIdentifier "fail")))
, ESymbol Rel "="
, ESqrt
    (EOver
       False (EIdentifier "content") (EPhantom (EIdentifier "fail")))
]
>>> tex
\sqrt{content} = \sqrt{\underset{\phantom{fail}}{content}} = \sqrt{\overset{\phantom{fail}}{content}}