This example visualizes population over time by region, displaying multiple lines that trend across a time axis with a categorical color legend. It uses D3 v5 APIs including `d3.nest`, `d3.scaleTime`, `d3.scaleLinear`, `d3.line`, and `d3.axisBottom` to render an SVG chart. Data is melted from UN population estimates and medium-variant projections, combining CSV sources. A custom color legend module and `mix-blend-mode` styling enhance readability, while axis labels and tick formatting clarify the scales.