sup element represents a superscript and the
sub element represents a subscript.
These elements must be used only to mark up typographical conventions with specific meanings, not for typographical presentation for presentation's sake. For example, it would be inappropriate for the
sup elements to be used in the name of the LaTeX document preparation system. In general, authors should use these elements only if the absence of those elements would change the meaning of the content.
In certain languages, superscripts are part of the typographical conventions for some abbreviations.
<p>The most beautiful women are <span lang="fr"><abbr>M<sup>lle</sup></abbr> Gwendoline</span> and <span lang="fr"><abbr>M<sup>me</sup></abbr> Denise</span>.</p>
sub element can be used inside a
var element, for variables that have subscripts.
sub element is used to represents the subscript that identifies the variable in a family of variables:
<p>The coordinate of the <var>i</var>th point is (<var>x<sub><var>i</var></sub></var>, <var>y<sub><var>i</var></sub></var>). For example, the 10th point has coordinate (<var>x<sub>10</sub></var>, <var>y<sub>10</sub></var>).</p>
Mathematical expressions often use subscripts and superscripts. Authors are encouraged to use MathML for marking up mathematics, but authors may opt to use
sup if detailed mathematical markup is not desired. [MATHML]
f(<var>x</var>, <var>n</var>) = log<sub>4</sub><var>x</var><sup><var>n</var></sup>