I've just looked at the beginning of Guido Henkel's book, and at his blog:
http://guidohenkel.com/2010/12/take-...ok-formatting/
Can't say I'm very impressed. He's purporting to 'solve' a lot of problems that would never arise in a document properly laid out in a word processor. And if you can't cope with paragraph and header styles in a WP, how are you suddenly going to grasp CSS and HTML styling in Sigil?
"However, I have never seen a book where the font size
suddenly jumped, where the font face suddenly changed,
where indentations were all over the place or where
paragraph adjustments switched from justified to right ragged
halfway through a page.
Since the dawn of eBooks, however, these things have
become prevalent What's even more worrisome is the fact
that to many authors this seems to be completely acceptable."