This capture shows you some of the different characters available in an OpenType font. This font, Contenu Book, has oldstyle figures [lowercase], lining figures [caps], & small cap figures. It also has true small caps, discretionary ligatures, ornaments, ordinals, and more. These things are always supposed to be used in print, even though only InDesign and Quark support such a thing for page layout AFAIK.
I assume most of you know this, but I thought I’d mention that ePUBs prefer OpenType fonts, though they will accept TrueType.
That means you not only need a license which allows ePUB embedding, but you also need fonts with an .otf [OpenType] or .ttf [TrueType] extension. PostScript fonts, the old printing standard, are simply dropped if you try to embed them.
The problem is that OpenType features do not work yet in ePUBs
So, for the present, you are limited to the basic 256-character set. I call this an 8-bit font. ePUB3 does support OpenType features, but it hasn’t been implemented anywhere yet. So, that will require hand coding for a while at least.