This example presents a course prerequisite tree as a static, pre-positioned node-link diagram. Users can click circular nodes to select courses, which highlights all related links and appends the course label to a sidebar list; clicking again deselects it. The visualization uses D3 v5, with an SVG renderer, vertical link paths via `d3.linkVertical`, explicit x/y coordinates per node, and CSS class-based styling for link highlighting. It uses a JSON data file containing nodes with levels and class attributes.