[Katsunami]

@Kovid: looks to be a great start already.

I'll make a counter offer.

I don't feel comfortable enough yet to program essential stuff like opening and saving books, keeping the NCX and OPF correct and that sort of thing, even if Calibre can already do it partly. If you can get the basics done to a point that a book can be opened, the HTML/CSS code and TOC edited (probably using the Edit TOC plugin), and saved again reliably, I will then start extending the editor with relatively simple extra functionality such as Clips/Snippets. I'll start there, because a mistake in such a function will probably not kill the book. From there, I'll work my way up toward the more "dangerous" functions such as merge/split, adding files (this stuff needs OPF adjustment).

Later on, I'll look at incorporating stuff like Tidy and Flightcrew again.

Eventually, Tweak Book will catch up to Sigil, and then it "only" needs to be maintained, and can be extended when needed. Probably this editor will have plugin support automatically through Calibre. I assume one can call Modify EPub if it's installed, instantly adding great clean-up power.