This example shows a Sankey diagram with five nodes and seven links, where the width of each link is proportional to its value, and nodes can be dragged to rearrange the flow. The visualization is built using D3 v4 and the `d3.sankey()` plugin, which handles node layout and link computation, while the SVG rendering uses `d3.select()` to append paths and rectangles. The code uses `d3.drag()` for interactive node movement, and the data is loaded from a JSON file with `d3.json()`.