@odamizu...I didn't include checks for epub 3 for several reasons. First, standard epub 3 is essentially html5 snd can be checked using Epubcheck. For Kindle epub 3 you would have to include checks for KF8 and KFX which is Kindle's own brand of fixed format. I also found that the differences between KFX, KF8 and standard epub 3 were badly documented and unreliable. That's really why my plugin doesn't check Kindle epub 3 ebooks.
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