<sub> for superscript

<sub> element denotes subscripts.

 
<!DOCTYPE HTML> 
<html> 
    <head> 
        <title>Example</title> 
    </head> 
<body> 
    x<sub>10</sub> is the 10<sup>th</sup>. 
</body> 
</html>
  
Click to view this demo.
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