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

<math xmlns="http://www.w3.org/1998/Math/MathML" display="block">  <mover>    <mi mathvariant="normal">B</mi>     <mi mathvariant="normal">long over script</mi>   </mover>   <mo>=</mo>   <mover>    <mrow>      <mi mathvariant="normal">B</mi>
    </mrow>     <mrow>      <mi mathvariant="normal">long over script</mi>
    </mrow>   </mover> </math>