How to find text in iBooks?!?!?

From what I've read, iBooks can find a word/phrase WITHIN a PDF/book if you happen to have that opened. But how do you search for a word/phrase in ALL your iBooks/PDFs when you're not sure which one it's in? When I use the main search bar, all it finds is book/PDF titles, but not any of the content of those files. Suggestions?