What it is for
The uses are concrete: writing a unit (m², km³), a chemical formula (H₂O, CO₂), a footnote marker (text¹) or a power — inside a field with no equation editor: a message, a bio, a filename, a spreadsheet cell.
Digits all work, letters only partly
This is the limit to know. All ten digits exist in both superscript and subscript, along with + − = ( ). Letter coverage is incomplete: superscript offers nearly the full lowercase alphabet, but subscript only about fifteen (a, e, h, i, j, k, l, m, n, o, p, r, s, t, u, v, x). Missing letters pass through unchanged.
This is not formatting
In Word or an HTML editor, superscript is an attribute applied to a normal character. Here, ² is a separate character. Practical consequence: searching for "x2" will not find "x²", and a spell checker may underline the word. Use it only where there is no alternative.
Frequently asked questions
Why do some letters not convert to subscript?
Unicode only encoded about fifteen subscript letters, those used in scientific notation. The others simply do not exist.
Can I write a full chemical formula?
Yes for most: H₂O, CO₂ and C₆H₁₂O₆ all work, since every digit is available as a subscript.
Does it work in Excel?
Yes, they are ordinary characters. Beware though: a superscript digit is no longer a number to Excel and will not be calculated.