<<< mml
<?xml version="1.0" encoding="UTF-8"?>

<math xmlns="http://www.w3.org/1998/Math/MathML">
  <msqrt>
    <mo>-</mo> 
    <mn>1</mn> 
  </msqrt> </math>
>>> native
[ ESqrt (EGrouped [ ESymbol Bin "-" , ENumber "1" ]) ]