HTML Encyclopaedia

The sub tag

The HTML element

<sub> text </sub>

tells the browser to render the text as a "subscript" as shown below.

The elements of a matrix may be referred to as a_ii ... a_nn

Here's the HTML for the line above

The elements of a matrix may be referred to as a<sub>ii</sub> ... a<sub>nn</sub>

The effects of including futher <sub> tags within subscript text are unpredicatable - but here goes

a_i a_{i_i} a_{i_{i_i}} a_{i_{i_{i_i}}}

Browsers
NN3 seemed capable of indefinite subscripting. IE3 could only manage two levels of subscript and IE4 and MOS3 could only manage a single level. OP2 and ARA ignored the tag.

See also <sup> and the general notes about text styles.