This is probably an edge case, but I work in lab software that uses chemical symbols and having sub and super characters saves lots of headaches. I can just store "CO₂" in a database, query it, and display it back as a simple string, or display values in scientific notation like 1,3×10³, without having to use any formatting.
But to be honest I'm not sure what the parent comment wants to see added because at the moment having all the letters from A-Z, numbers from 0-9, and plus minus and equals signs as both subscript and superscript seems to be enough.
But to be honest I'm not sure what the parent comment wants to see added because at the moment having all the letters from A-Z, numbers from 0-9, and plus minus and equals signs as both subscript and superscript seems to be enough.