This example shows an interactive force-directed graph of hierarchical data from a JSON file, where nodes represent categories and files, and links show parent-child relationships. Users can collapse or expand nodes by clicking, which restarts the layout simulation. The visualization uses the `d3.layout.force` API to compute node positions and link distances, with node size mapped from the data’s `size` attribute. Rendering is done via SVG, with circle styling and text labels per node, and the color function distinguishes collapsed, expanded, and leaf nodes.