The library seems to work fine for ex-post-facto markup of already-entered text. That is, select some text, press an underline button, and it underlines that text. But it does not seem to have any concept of changing the style at the insertion point.
Normally, when editing in a rich text situation, if there's no selected span, that button indicates "going forward from the current insertion point, text will be underlined".
Am I just not getting something obvious? (That's certainly likely. 🙂 )