Certain generated epubs do not read with google books

[mrothbart]

Heretical edge, Vacant Throne, Fifth Defiance, saga of soul all produce ebooks that can be read with calibre but not google books. I am unclear as to why that is.

Deathworlders simply errors out without producing anything.

[kemayo]

I don't have easy access to google books to test this -- is it very unfriendly to epubs with minor validation errors? The approach taken here of downloading arbitrary HTML and cramming it into an epub makes it easy to wind up with e.g. unsupported properties.

[kemayo]

Saga of Soul had some obvious issues with namespaced elements, so I added some filtering for that. Vacant Throne had some messed up indexing which might have been confusing matters, I guess? So I fixed its example somewhat.

[mrothbart]

What I did to create a valid Vacant THrone epub was to save the HTML in a file, strip all href and tags besides for the ToC, then serve it locally from a WSL server and point the script at it. It worked great, but obviously not scalable.