A hierarchical circle-packing visualization displays nested data as clustered bubbles, with zooming and panning via mouse clicks. The demo uses D3.js v5 to construct the SVG layout, apply an HSL color scale by depth, and animate transitions between hierarchy levels using `transition` and `interpolateZoom`. Buttons add or remove data nodes, while the pack layout is generated with `d3.pack` and `d3.hierarchy`. The dataset is hardcoded from a “flare” file structure.