This example visualizes population over time by region, with multiple lines colored by region and ordered by their final values. The chart uses a time scale for years, a linear scale for population, and an ordinal color scale with a custom legend. It demonstrates data melting by transforming wide-format CSV rows into long-format records via `d3.range` and nested loops, then draws the lines with `d3.line` and `curveBasis`. The tooltip-free SVG rendering relies on D3 v5 APIs, including `d3.nest`, `extent`, `axisLeft`, `axisBottom`, and `d3.format`.