The <sup>. . .</sup> tags cause
text that occurs between them to be displayed as a superscript, as in
mathematical equations and footnote references.
<sup> Example
This markup:
Pythagorean Theorem:
x<sup>2</sup> + y<sup>2</sup> = z<sup>2</sup>
. . .according to recent research<sup>[1]</sup>,
evidence shows. . .
. . .causes the following to be displayed:
Pythagorean Theorem:
x2 + y2 = z2
. . .according to recent research[1],
evidence shows. . .