title_body: EpubCheck in Calibre gives errors with epub:type and aside I get these two errors:
  
  ERROR(RSC-005): Error while parsing file 'attribute "epub:type" not allowed here;
  
  ERROR(RSC-005): Error while parsing file 'element "aside" not allowed anywhere;
  
  How can I remove them? I want to use pop-up footnotes with epub3.
  
  Regards Dan
upvoted_answer: epub:type attributes can only be used in epub3 books. You'll need to select Polish books > Upgrade book internals to convert your epub2 book to an epub3 book.