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jpomart - apologies for confusing you - my reference to those settings in the Word add-in was intended as a hint to the other aficionados - IIRC those two radio buttons are used to create Sigil and Calibre 'compatible' code - something to do with entities. But it was another existentialist red herring
You can split the EPUB into several XHTML files within Sigil - a common practice is to split on chapter boundaries.
BR