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

<math xmlns="http://www.w3.org/1998/Math/MathML">
  <mrow>
    <mi>x</mi> 
    <mo>+</mo> 
    <mi>M</mi> 
    <mo>+</mo> 
    <mi mathsize="2em">x</mi> 
    <mo>+</mo> 
    <mi mathsize="2ex">x</mi> 
    <mo>+</mo> 
    <mi mathsize=".1in">x</mi> 
    <mo>+</mo> 
    <mi mathsize=".5cm">x</mi> 
    <mo>+</mo> 
    <mi mathsize="8mm">x</mi> 
    <mo>+</mo> 
    <mi mathsize="24pt">x</mi> 
    <mo>+</mo> 
    <mi mathsize="2pc">x</mi> 
    <mo>+</mo> 
    <mi mathsize="75%">x</mi> 
    <mo>+</mo> 
    <mi mathsize="36pt">x</mi> 
  </mrow> </math>