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

<math xmlns="http://www.w3.org/1998/Math/MathML">
  <mi>H</mi> 
  <mover>
    <mo>&#x2192;</mo> 
    <mtext>This is a long stretched arrow</mtext> 
  </mover> 
  <mi>H</mi> </math>