The only way I know of doing this in any RoboHelp version:
1. Select the text you want to set to superscript.
2. Go to HTML view
3. Put the selected text between sup tags: My suptertext
4. Save and to back to WYSIWYG.
In the RoboHelp editor, the supertext will have the regular font size but it will be aligned differently. When you create your output, the superscript is shown correct.
Please file a feature request if you also want Adobe to provide buttons for creating superscript and subscript. There is a link to the feature request form in the Useful links section in the sidebar of the forum.
It seems the tags didn't come trought correctly via mail reply:
- Put the selected text between sup tags: <sup>My supertext</sup>
As Peter reminded me, there is also a CSS style you can use for a character style: vertical-align: super; You will have to manually edit your css for this. See also: http://www.w3schools.com/cssref/pr_pos_vertical-align.asp
If you need supertext only as a presentational element, you can use the CSS. If the supertext/subtext also conveys meaning (for instance for chemical formula's), I would recommend the sup tag. The sup tag gives semantical information that may be picked up by screen readers etc.