Subscript

This (respectively) sets the text slightly below the normal line height.
Subscript text appears below the baseline, smaller than the regular text.
Most often used in formulas and equations but can serve any other purpose aswell.

pencil BBCode usage

[sub]{TEXT}[/sub]

html5 HTML replacement

<sub>{TEXT}</sub>

question Help line

Subscript: [sub]text[/sub]

Examples

I can't develop any more custom extension, I am starting to see blurry;[sub];[sub];[/sub][/sub]

I can’t develop any more custom extension, I am starting to see blurry;_;;

The formula for the Dioxygen compound (the Oxygen molecule) is: O[sub]2[/sub].

The formula for the Dioxygen compound (the Oxygen molecule) is: O₂