Kobo Nickel css styles

I'm currently trying to figure out why .kepub's generated by KCC do not support bookmarking/annotations and it seems to be related to the various css classes and other document properties.

Eg: Adding span's around images with the class "koboSpan" and dropping pre-paginated meta property enables full functionality, but that brings with it another downside: no full screen images, there is always a margin applied.

Does anyone know where I can actually find information on these kobo classes?