Since Marvin 3.0 was released on June 20, 2016, it has claimed to support EPUB 3.0 on its App Store description page:
Marvin opens DRM-free EPUB books (basic support for 3.0), and CBZ/CBR comics.
Since then, seven updates has been released over the last two months, and yet the so-called basic support can't even extract Table of Contents from the standard
EPUB 3.0 test cases. (See also
this thread).
Therefore, I strongly advise kguil to drop the claim of "basic support for (EPUB) 3.0" so as not to be misleading. He can always add it back in the future whenever the basic support is really there.