How to show text as a superscript in Alt text

like开发者_如何学运维 this:

Value¹⁰

Like the knittl and SLaKs said, try unicode character html entities.
http://en.wikipedia.org/wiki/Unicode_subscripts_and_superscripts

¹²³⁴⁵⁶⁷⁸⁹⁰

Result: ¹²³⁴⁵⁶⁷⁸⁹⁰

Bigger: ¹²³⁴⁵⁶⁷⁸⁹⁰

Though, for the sake of readability, you might just want to do something like 10^1234.
Or, for citations, whatever[1].

alt text is just normal text, you can try to insert unicode supertext characters:

Value¹⁰

but it will depend on the font of the viewer (and proper encoding) if it works

You can't; alt text only supports plain text without formatting.

However, you can fake it with Unicode characters. (¹⁰)