This example shows a hierarchical dataset with nested nodes (A1, B1, C1–C3, B2) displayed as a circle-packing layout, where each node’s bubble size reflects its numeric value. The code uses D3’s `d3.pack()` and `d3.hierarchy()` to compute the layout, with `rootNode.sum()` summing child values for sizing. An SVG canvas is created and sized to the container, and descendant nodes are selected for rendering. The visualization relies on D3 7.8.5 and the `index.js` module exports a `main` function that drives the layout generation and SVG setup.