Due to development of other manuals like ours, a page with "Table of contents" has been added, with the section #0. "Introduction" remains section #1, which has the advantage that the TOC section is always present in the sidebar. So now with 2 clicks you can go to any page you want.
This improves the navigation inside the manual tremendously, that I wonder that I haven't done it much earlier! The sidebar remains as it is, with showing "nearby" sections of the current page to keep it short. The complete TOC is of course much longer.
