@chris.prener
I probably make it more confusing than I needed to be.
What I have right now using #, ##, and ### is roughly fine:
1- Section ABC
1.1- A subsection
1.2- Another one
1.3- A third one
1.3.1- A sub-subsection
1.3.1- Another one
2- Section DEF
2.1- Some subsection
2.2- Another one
If I transform my sections into parts, my subsections into sections, and my sub-subsections into subsections, I get:
Section ABC
1- A subsection
2- Another one
3- A third one
3.1- A sub-subsection
3.1- Another one
Section DEF
4- Some subsection
5- Another one
I would need the section numbering to reset within parts... which is impossible. So I will keep using the first approach but will add the following css to allow TOC text to wrap when it is larger than the panel width:
.book .book-summary ul.summary li a, .book .book-summary ul.summary li span {
white-space: normal;
}