[Ripplinger]

I'm finishing up an epub I scanned from an old book (it's in the public domain), and I was curious about using html, or should the files all be xhtml? Does it make any difference?

When I open up purchased books where I know there's been no tampering or conversions to check what was used, some books are all xhtml, some are all html, and some are a mix of both file extensions within the book. So that was no help at all for me.

Is there really a standard it should be and what's the difference between the two?