[ibu]

Thanks for the hint about the cover image.
I added the attribute "properties".

And I separated the the nav.

The validated attachement contains the changes. When we finishe this thread, I will edit the first posting and will attache the final file so it is easier for readers to find the latest version.

The cover is not visible in the Kobo. Nor it is the TOC.
But I haven't started with the work to make the minimal epub3 compatible to KOBO. That may be the reason.

Is it true, that the nav must appear inside the spine element? It couldn't find information about that in the specs.

About the validator:
May be it would be useful, when it warns, if a nav does not exist as a separated file?