This nifty little option outputs to stderr what the header graph looks like!
Sample output excerpt for this document:
= h1 ourbigbook == h2 1 quick-start == h2 2 design-goals === h3 2.1 saner === h3 2.2 more-powerful == h2 3 paragraphs == h2 4 links
This option can also serve as a debug tool for header tree related features (confession: that was its original motivation!).