Specifications for epubs for the iPad? Does someon has information?

[georg3200]

Hi there,
We produce epubs for our customers, mostly for publishers. Now all customers want the epubs to work on the iPad. We have an iPad and our epubs work on it, but what if we want to sell them in the Apple Store (iBooks iTunes or whatever).

I'm quite sure that apple has specifications / guidelines for epubs. But, I do not find anything on the web. I only find the link to apply a someone who wants to sell ebooks on iTunes. But one the one hand, we do not want to sell ebooks and on the other hand we are a German company and only American companies can apply...

So I do not really know what Apple wants a epubs to look like. I know some tricks like "how do I make the frontcover visible" and "page-breaks don't work" but I am quite sure that that is not enough.
Probably they want it to pass epubchecker 1.05.... but is that enough?

Can someone help me? Does someone know their specifications?