Try using epubcheck on those to see where the finger really should be pointed. There are a lot of really crap "epubs" out there. https://www.w3.org/publishing

Try using epubcheck on those to see where the finger really should be pointed. There are a lot of really crap "epubs" out there. https://www.w3.org/publishing/epubcheck/ https://www.w3.org/publishing/epubcheck/