This example demonstrates how to group and structure an array of car objects using the `d3.nest()` function. It defines four car records with name, manufacturing year, and model, then applies a key function on the `manufactured` property to create hierarchical groups. The resulting nested data structure is logged to the browser console, showing how entries are organized by year. The code uses D3 version 4 and executes entirely in the console without any visual rendering on the page.