Special characters / HTML modifiers in channel descriptions

I tried to insert special characters in my channel descriptions. I succeeded in using Unicode characters by using the numbered code, so eg. ³ for a 3 superscript (cubic).
This does not work for subscripts as there aren’t in the Unicode character table. Is it possible to use HTML modifiers for that? Concretely I try to do a numbered subscript, eg. like in H2O. If HTML were permitted, I would write it as H<sub>2</sub>O, but it did not work like this. Any idea?

No, only Unicode is possible.

For anyone with the same problem:
Differently than I wrote before, Unicode with numbered code is also not allowed (while testing it I still used an old file). The only thing that works is UTF-8 encoding of the xml or properties file. This has to match the first line of the .xml file (<?xml version="1.0" encoding="UTF-8"?>).