When the heading of a 'parent' page (a page with some child pages on the same topic) is clicked on in the navigation bar, it just toggles folding of that section of the nav bar.
This is not helpful, since these 'parent' pages have unique content that a user may wish to read - they are not simply topic headings in the navigation bar. The only way to get to these pages seems to be to click on the 'breadcrumb trail' link at the top of the page, which is unintuitive and frustrating.
It would be better if the nav bar allowed direct navigation to these pages. Folding/unfolding should be triggered only by a click on the '+' or '-' prefix of a listing in the nav bar.