As a side effect, superscripts often cause lines to be unevenly spaced.
The notation A<SUP>T</SUP> denotes the transpose of A.
Consider the equation x<SUP>n</SUP> + y<SUP>n</SUP> = z<SUP>n</SUP>.
The expression a<SUP>b<SUP>c</SUP></SUP> means a<SUP>(b<SUP>c</SUP>)</SUP>.
This example is a text paragraph which contains several superscripted expressions such as m<SUP>2</SUP> and e<SUP>x</SUP>. They may affect the visual appearance of the paragraph by forcing the browser to use different line heights. This applies in particular to expressions with large and nested superscripts such as (f(a))<SUP>e<SUP>x<SUP>2y</SUP></SUP></SUP>.
Non-mathematical examples:<BR> The word "first" can be written as 1<SUP>st</SUP>.<BR> Foo<SUP>(TM)</SUP> is a trademark of Bar, Inc.<BR> In French, the word "mademoiselle" is abbreviated M<SUP>lle</SUP>.
There is also an element for subscripts, SUB, but HTML 3.2 provides no general support for mathematical formulas.
Since this element is new, support for it is not universal.
Some browsers simply ignore it, displaying e.g.
And naturally, text-only browsers cannot truly support SUP.
Superscripts can be nested, as the last example shows. This may, however, result e.g. in rendering inner superscripts in a very small font. Internet Explorer ignores SUP tags after nesting level of two.
See also general notes on text markup.