-<li><a href="#sec-1">1. System requirements</a></li>
-<li><a href="#sec-2">2. Installation</a></li>
-<li><a href="#sec-3">3. Scene description language</a></li>
-<li><a href="#sec-4">4. Usage</a></li>
-<li><a href="#sec-5">5. Examples</a>
+<li><a href="#sec-1">1. General</a>
+<ul class="nav">
+<li><a href="#sec-1-1">1.1. Source code</a></li>
+</ul>
+</li>
+<li><a href="#sec-2">2. Operating principle</a></li>
+<li><a href="#sec-3">3. System requirements</a></li>
+<li><a href="#sec-4">4. Installation</a></li>
+<li><a href="#sec-5">5. Scene description language</a></li>
+<li><a href="#sec-6">6. Usage</a></li>
+<li><a href="#sec-7">7. Examples</a>