Nicolas,

2013/12/9 Nicolas Goaziou <n.goaziou@gmail.com>

> #+HTML_HTML5_FANCY: t
>
> in level-0.org

There is no such keyword. Use:

#+OPTIONS: html5-fancy:t

or set `org-html-html5-fancy' to a non-nil value.

Thanks. I copied that line from here:
http://orgmode.org/worg/org-tutorials/org-publish-html-tutorial.html#sec-5

I don't know of this constitutes a bug in the document using that keyword, but that is something that misled me.