Some wiki engines offer markup for superscript and subscript text.

!!Superscript

%%(vertical-align: sup) Superscripted %% text


Creole: {{{ ^^This is superscripted text^^ }}}

Proposed XHTML: {{{ <sup> </sup> }}}

Comparsion:
http://www.wikimatrix.org/syntax.php?i=28

!!Subscript

%%(vertical-align: sub) Subscripted text %%

Creole: {{{ ~~This is subscripted text~~ }}}

Proposed XHTML: {{{ <sub> </sub> }}}

Comparsion on wikimatrix:
http://www.wikimatrix.org/syntax.php?i=29