Subscript

From AmericolaWiki

An example of subscripts
A_bC_d

A subscript is a number, figure, or indicator that appears below the normal line of type, typically used in a formula, mathematical expression, or description of a chemical compound. Probably the most famous example of a subscript is the number 2 in the formula for the molecule of water: H₂O.

Typographically, subscripts are set using a lower baseline and a smaller size than the other text. For example, to set H₂O correctly, the 2 should be about 2/3 the size of the H and the O. This is done automatically in many text editing and word processing programs.

In HTML and Wiki syntax, subscript text is produced by putting it inside the tags <sub> and </sub>.
Unicode defines subscript characters such as ₀ ₁ ₂ ₃ ₄ ₅ ₆ ₇ ₈ ₉ ₊ ₋ ₌ ₍ ₎ (&#8320 to &#8334).
In TeX's math mode (as used in MediaWiki), subscripts are typeset with the underscore _: $X_{ab}$ produces <math>X_{ab}</math>.